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When you’re looking for the ultimate restaurant-quality burger to make at home, turn to these Caramelized Onion Burgers. Featuring crispy smash burger patties, caramelized onions, mustard-y sauce and melty havarti, each bite is true perfection.
I grew up on burgers—we had them weekly—so I know my way around a burger. And while the burgers I grew up on were very classic American (think lettuce, tomato, onion, and cheese), my burgers these days tend to be a bit more unique while still being simple and approachable.
Smash burgers are my go-to because of their foolproof method. I like to top them with my simple burger sauce, but sometimes you need a little extra something. So when the Iowa Beef Council asked me to lead a Bourbon & Beef cooking demo at the Iowa State Fair, I knew where I wanted to start.
I start with bourbon-infused caramelized onions that get piled onto the smash burger patties with melty havarti cheese and mustard-based burger sauce. Each bite is so dang good.
Caramelized Onions for Burger
The list of potential burger toppings is endless (same goes for chili toppings). But a mainstay is caramelized onions. You can never go wrong! Caramelized onions are the king of burger toppings and can take center stage or simply be a supporting character.
Keep it simple, like we’re doing here, and serve the burgers with just cheese, caramelized onions and a burger sauce. Or load up the caramelized onion burger with sautéed mushrooms, bacon and/or avocado.
My recipe for caramelized onions is fairly straightforward featuring brown sugar, bourbon and Worcestershire. The results are caramelized onions that are deeply flavored and just sweet enough.
Ingredients for Grilled Onion Burger
Caramelized Onions for Burgers
- Olive oil: I like the consistency of browning that olive oil offers when cooking onions. However, you can use butter instead of oil or you can use both olive oil and butter for the best of both worlds.
- Kosher salt: you need a dash of salt to balance out the sweetness of the onions!
- Onions: I prefer to use regular onions here. You can also use white or vidalia.
- Brown sugar: dark or light works here. Dark brown sugar will add a deeper flavor while light brown sugar will allow the bourbon to shine through a bit more.
- Bourbon: a generous glug of bourbon adds flavor and nuance to the caramelized onions. You can substitute it with apple juice.
- Worcestershire sauce: a splash adds depth, umami and nuance to the caramelized onions. Don’t skip this!
Burger Sauce
- Whole-grain mustard: whole grain mustard pairs wonderfully with caramelized onions. You can also use stone ground, but you’ll miss out on the lovely pops of texture that whole-grain mustard adds.
- Dijon mustard: adds a spicy, tangy kick to the creamy sauce.
- Mayonnaise: cuts the tangy, bold flavor of the two mustards and makes a lusciously creamy spread.
- Red wine vinegar: just a splash is needed to brighten up the burger sauce.
Burgers
- Ground beef: I recommend using 80/20 . The fattier the beef, the more flavorful it will be. But on the flip side, the leaner the beef is the less the patties will shrink and splatter during cooking.
- Buns: I like to use brioche buns because they’re soft, tender, buttery and slightly sweet.
- Havarti cheese: you’ll need deli-slices for these burgers. If you can’t find havarti slices, use provolone or swiss.
How to Make Caramelized Onion Burgers
Make the Caramelized Onions for Burgers:
- Slice the onions into thin wedges, from root to stem. The onions will break down and become more jammy if they are sliced this way as opposed to crosswise.
- Soften the onions in a sauté pan with some olive oil. Season with salt and continue to cook until softened and translucent.
- Add the brown sugar and continue cooking until the onions are jammy and deeply golden brown, this will take about 30 minutes. You may need to add water, by tablespoon measure, to keep the onions from burning and sticking to the pan.
- Once the onions are caramelized, add the bourbon and Worcestershire sauce and cook until the liquid has evaporated, about 2 minutes. Remove the pan from the heat and season with salt and pepper to taste.
Cook the Burgers:
- Pre-Smash the Patties: this makes the cooking process faster. Smash the balls of ground beef between two pieces of parchment paper until they are about ¼-inch thick.
- Cook the Burgers: season one side of the patties with salt and place salted side down on the hot steel, flat-top or cast-iron skillet. Season tops of patties and smash, pressing down hard, to sear the meat and keep the patties flat.
Flip the patties and top with caramelized onions and a slice of cheese. Cover and cook until the cheese is melted.
- Assemble the Burgers: spread a generous dollop of the sauce on both the cut sides of the buns. Place the burger on the bottom bun then place the top bun on top. Serve immediately.
Caramelized Onion Burger Tips
- Fat percentage of beef matters: the fattier the ground beef, the more flavor it will have. It also directly correlates to how much the burger patties will shrink during cooking. We recommend 80/20 or 85/15 beef.
- Pre-smash the patties: pre-smashing the patties makes for a quicker and easier cooking process. I recommend smashing the patties between pieces of parchment. This will keep them from sticking together and will also make it easier to transfer the smashed patties to the hot cooktop.
- If your onions are burning, simply add a splash of water to the pan and scrape up the browned bits using a wooden spoon. This adds even more flavor!
- To caramelize the onions faster, you can add a pinch of sugar. This will help the natural sugars in the onions begin to turn golden brown.
How to Serve Onion Burgers
Fries are a classic pairing! My favorite homemade fries are the frites from my Steak Frites recipe. Or try Polenta Fries for something a bit more unique.
Then pair it all with a light and crunchy Carrot Cucumber Salad. It’s fresh and crunchy—the perfect contrast to a juicy, decadent smashburger.
Storage and Make Ahead
Store any leftover burger patties in an airtight container in the fridge for up to 3 days. Reheat in the microwave or stovetop until warmed through.
You can make the caramelized onions in advance, they keep in the fridge well for up to 4 days. Reheat in a skillet with a splash of water until warm. If you make the onions in advance, the burger recipe takes only 10 minutes to prepare!
More Burger Recipes
Grilling & BBQ
Hawaiian Pineapple Burger
Sandwiches
How to Cook a Smash Burger at Home
Fish & Seafood
Fresh Shrimp Burgers
Caramelized Onion Burger
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Ingredients
Caramelized Onions
- 4 teaspoons olive oil
- 4 medium yellow onions, sliced into thin wedges root to stem
- 1 teaspoon kosher salt
- 2 tablespoons packed brown sugar
- 3 tablespoons bourbon
- 2 teaspoons Worcestershire sauce
- Freshly ground black pepper
Burger Sauce
- ¼ cup Dijon mustard
- ¼ cup whole-grain mustard
- ¼ cup mayonnaise
- 1 teaspoon red wine vinegar
Smash Burgers
- 1 pound ground beef (80/20 or 85/15)
- kosher salt
- 4 brioche buns, split
- 4 slices havarti cheese
Instructions
Caramelized Onions
- In a large sauté pan, heat olive oil over medium. Add onions, stir to coat, then cook, stirring occasionally, until starting to soften but not brown, about 10 minutes. (Depending on the size of your pan, you may need to add onions incrementally as the onions cook down and space in the pan becomes available.)
- Add salt and stir to coat then cook, stirring occasionally, until onions soften, about 10 minutes. Add sugar and stir to coat, continue cooking until jammy and deeply golden brown, about 30 minutes. You may need to add water, by tablespoon measure, to keep onions from burning and sticking to pan.
- Once caramelized, add bourbon and Worcestershire sauce and cook until liquid has evaporated, about 2 minutes. Remove from heat and season with salt and pepper to taste.
Burger Sauce
- In a medium bowl, whisk together mustards, mayonnaise and vinegar; season with salt and set aside.
Smash Burgers
- Divide meat into quarters (about 4 oz. each) and roll into balls.
- Working with 1 ball at a time, place ball on a piece of parchment paper, top with a second piece of parchment paper and press into a ¼-inch thick patty using a burger press or iron. Repeat with remaining ground beef balls; layer pressed patties between parchment to avoid sticking together.
- Heat a large cast-iron, stainless steel, or carbon steel skillet (or flat top) over medium-high heat until ripping hot and smoking, about 5 minutes.
- Toast buns, cut side down, in skillet until lightly golden, about 1 minute.
- Increase heat to high. Season one side of patties with salt, place patties salted side down, in skillet; season generously with salt and cook, without moving but smashing lightly with burger iron to keep flat, until bottom sides are crisp and browned, about 1½ minutes.
- Flip patties then top with caramelized onions and a slice of cheese. Cover and cook until cheese is melted, about 1 minute.
- Wipe out skillet with paper towels before repeating cooking process with remaining beef patties, onions and cheese.
- To assemble, spread 1 tablespoon burger sauce on both cut sides of buns (tops and bottoms). Place patty on bottom bun then top with top bun and serve.
