10 tablespoon unsalted butter, frozen, and divided
1½ cups peeled, pitted, and diced fresh peaches
½ cup whole milk
½ cup sour cream
1 tablespoon pure vanilla extract
2 cups all-purpose flour (10 ounces)
⅓ cup granulated sugar (2 ½ ounces)
1 tablespoon baking powder
1 teaspoon ground cinnamon
½ teaspoon baking soda
½ teaspoon table salt
Heat oven to 425°F and adjust oven rack to middle position. Line baking sheet with parchment paper.
Grate 8 tablespoons butter on a large-hole grater. Separately freeze grated butter and diced peaches until needed. Melt remaining 2 tablespoons of butter and set aside.
Whisk together milk, sour cream, and vanilla in a medium bowl; refrigerate until needed. Whisk flour, sugar, baking powder, cinnamon, baking soda, and salt in a medium bowl.
Add frozen butter to flour mixture and toss with fingers until thoroughly coated. Add milk mixture to flour mixture and fold with spatula until just combined.
Transfer dough to a well-floured work surface. Dust dough with flour and knead 10 to 12 times until it forms a rough ball, adding flour as needed to prevent sticking.
Roll dough out into a 12-inch square. Fold dough into thirds over each other to create a 12×4-inch rectangle. Lift ends of dough and fold by thirds again to form a 4-inch square. Transfer dough to a plate and freeze for 10 minutes.
Roll chilled dough into a 12-inch square. Sprinkle frozen peaches evenly over surface and lightly press into dough. Roll into a tight log, ending with seam side down. Press log into a 12×4-inch rectangle. Cut log crosswise into 4 equal sections. Cut each section diagonally to form 2 triangles (8 triangles total). Transfer scones to prepared baking sheet.
Brush tops of scones with 2 tablespoons melted butter. If desired, lightly sprinkle tops with sugar for additional crunch.
Bake until tops and bottoms are deep golden brown, 25-30 minutes. Transfer to wire rack and cool completely.