1-First step: Prep the pan and oven Start by heating your oven to 350°F. Line a 9×13-inch baking pan with parchment paper, leaving a little overhang on the sides so you can lift the bars out later. This small step saves a lot of time when it is slicing day. If you want neat squares for a party tray, parchment is your best friend. While the oven heats, peel, core, and slice the apples into 1/8-inch slices. Thin slices help the fruit cook evenly and soften without turning mushy. Tart and sweet-tart apples work best because they hold their shape and give the bars a bright flavor.

2-Second step: Make the shortbread dough In a large bowl, stir together the flour, granulated sugar, light brown sugar, baking powder, and kosher salt. Add the 1 1/2 sticks of unsalted butter cut into 12 pieces. Use a pastry cutter, fork, or your fingers to work the butter into the dry ingredients until the mixture looks crumbly and sandy. You want small bits of butter throughout the dough for that rich, tender shortbread texture. If the mixture feels too dry, keep mixing gently. Shortbread dough should hold together when pressed, but it should not feel wet. That balance helps the base bake into a firm, buttery layer that can support the apple filling.

3-Third step: Press the crust into the pan Reserve about 1 cup of the dough for the topping, then press the rest firmly and evenly into the bottom of the lined pan. Use your hands or the bottom of a measuring cup to flatten it into the corners. A well-packed crust bakes more evenly and gives the bars a clean base. For a slightly lighter texture, do not overwork the dough. Press it just until it looks even. If you are baking for a crowd, this is also a good time to think about portion size. A 9×13 pan usually gives about 16 bars, which works well for potlucks and bake sales.

4-Fourth step: Mix the apple filling In another bowl, whisk together the eggs, granulated sugar, light brown sugar, flour, heavy cream, apple pie spice, and kosher salt until smooth. The mixture will look loose at first, but the flour and eggs help it thicken as it bakes. Stir in the sliced apples until they are well coated. The filling should smell warm and spiced right away. If you want a slightly bolder apple flavor, choose a mix of tart and sweet-tart apples. That gives the bars a nice balance and keeps them from tasting too sweet.

5-Fifth step: Assemble the bars Spoon the apple mixture evenly over the shortbread crust. Try to spread the fruit all the way to the edges so every square gets plenty of filling. Then crumble the reserved dough over the top. It does not need to cover every bit of apple. Those little open spaces let the fruit bubble up and create a pretty finish. This stage is simple, but it is also where the bars start to look bakery-worthy. If you are making them for a holiday table, the rustic top gives them a homemade charm that people always love.

6-Sixth step: Bake until golden Bake the bars for about 45 to 50 minutes, or until the top is lightly golden and the filling is bubbling around the edges. The apples should be tender when pierced with a knife. If the top starts browning too fast, loosely cover the pan with foil near the end of baking. Let the bars cool completely in the pan before cutting. This matters because the filling sets as it cools. If you cut them too soon, the slices may fall apart. For clean squares, lift the bars out using the parchment overhang and cut with a sharp knife.

7-Final step: Slice and serve Once cooled, cut the Brown Butter Apple Shortbread Bars into squares and serve them as they are, or dust them lightly with powdered sugar if you like a sweeter finish. They taste great warm, room temperature, or chilled. For a simple dessert plate, pair them with vanilla ice cream or a spoonful of whipped cream.