1-First Step: Heat the oven and brown the butter Start by heating your oven to 350°F. Place 1 1/2 sticks of unsalted butter in a skillet and melt it over medium heat. Keep cooking until the butter turns golden brown and smells nutty. Brown butter gives these Brown Butter Apple Shortbread Bars their deep flavor, so do not rush this part. If you are short on time or prefer a simpler method, you can use regular melted butter instead.

2-Second Step: Mix the shortbread dough Once the butter is browned, transfer it to a mixing bowl and stir in the kosher salt, all-purpose flour, granulated sugar, packed light brown sugar, and baking powder. Mix until a soft dough forms. It should feel crumbly but press together easily. This is the base for your apple shortbread bars, so make sure the dough is evenly mixed with no dry flour left behind.

3-Third Step: Press and bake the crust Line an 8×8-inch baking pan with parchment paper, leaving enough overhang to lift the bars out later. Press most of the dough firmly into the bottom of the pan to create an even layer. Bake the crust for 15 minutes, just until it looks set and lightly golden around the edges. If you want thinner shortbread bars, you can use a 9×9-inch pan, though the bars will bake a little thinner and may need a slight timing adjustment.

4-Fourth Step: Make the apple filling While the crust bakes, increase the oven temperature to 375°F. In a bowl, whisk together the eggs, granulated sugar, packed light brown sugar, all-purpose flour, heavy cream, apple pie spice, and kosher salt. The mixture should look smooth and creamy. Then fold in the sliced apples until every slice is coated. Use tart apples if you can, since they balance the sweetness of the filling so well.

5-Fifth Step: Layer the filling and topping Spread the apple mixture evenly over the baked crust. Crumble or scatter the reserved dough over the top. This gives the bars a rustic look and a nice shortbread finish after baking. If your apples are not very tart, a small splash of lemon juice can brighten the flavor and keep the filling from tasting too sweet.

6-Sixth Step: Bake until thickened and golden Bake the bars for 55 to 60 minutes, until the top is golden and the apple filling looks thickened and set. The center should no longer look loose or wet. If you are using a pan with a different size or a very juicy apple variety, check the bars near the end of baking and add a few extra minutes if needed.

7-Final Step: Cool, slice, and serve Let the Brown Butter Apple Shortbread Bars cool completely in the pan before lifting them out and cutting them into 12 to 16 pieces. Cooling matters because the filling firms up as it rests. If you cut too soon, the bars can fall apart. Once cooled, serve them plain or with a light dusting of powdered sugar if you like a bakery-style finish.