Heat oven to 350ºF (176ºC) with rack set in middle position.
Grease an 8×8-inch metal baking pan with nonstick spray; line pan with 1 piece of parchment paper to form a sling.
In a medium bowl, whisk together flour, oats, salt, baking powder and cinnamon.
Cut butter into tablespoons and add to a large bowl. Microwave butter in 30 second increments until melted.
Add coconut sugar, peanut butter and vanilla to warm melted butter and whisk until smooth; about 30 seconds. Let rest 1 minute, then whisk another 30 seconds. Rest 1 minute then add egg yolks.
Whisk until a smooth caramel-like batter is formed. Scrape whisk clean.
Add flour mixture to peanut butter mixture and, using a rubber spatula, mix until a dough comes together.
Roughly chop chocolate chips and chocolate candies; reserve 2 tablespoons for sprinkling over top.
Add remaining chocolate chips and chocolate candies to dough and mix to combine.
Press dough into prepared pan in an even layer using hands.
Sprinkle reserved chocolate and candies over top.
Bake cookie bar until edges are lightly browned and center is puffed but set, 17–20 minutes. (Don’t over-bake!)
Transfer pan to a wire rack and sprinkle bar with flaky sea salt, if using.
Let bar cool in pan 10 minutes. Lift bar out of pan using parchment overhang and transfer to wire rack to cool completely.
Using a large sharp knife, cut bar into 9 squares.