Preparation

1. Streusel

   Step 1

   Preheat your oven to 350°F and place a rack in the middle. Lightly coat an 8x8" metal baking pan with nonstick vegetable oil spray, and line it with parchment paper, leaving an overhang. Lightly spritz the parchment with nonstick spray. Combine 1¼ cups (156 g) all-purpose flour, 1 cup (packed; 200 g) light brown sugar, 1½ tsp. Diamond Crystal or ¾ tsp. Morton kosher salt, 1½ tsp. ground cinnamon, ½ tsp. baking powder, and ½ cup (1 stick) unsalted butter, melted in a large bowl, mixing with hands until marble-sized clumps form. Set this streusel aside.

2. Cake and assembly

   Step 2

   In a large bowl, toss together 1 lb. Honeycrisp apples (approximately 2 large), peeled, cored, and thinly sliced with 2 Tbsp. (16 g) all-purpose flour.

   Step 3

   In another large bowl, whisk together 1 cup (200 g) granulated sugar, 1½ tsp. Diamond Crystal or ¾ tsp. Morton kosher salt, 1½ tsp. baking powder, ¼ tsp. baking soda, and the remaining 1⅔ cups (208 g) all-purpose flour. Add ½ cup (1 stick) chilled unsalted butter, in pieces, and rub into the dry ingredients until no visible pieces remain. Once mixed, add 2 large eggs, ⅔ cup buttermilk, 2 Tbsp. vegetable oil, and 1 Tbsp. vanilla extract. Stir until no dry flour remains, for about a minute, then fold in roughly two-thirds of the apple slices.

   Step 4

   Pour the batter into the prepared pan, spreading it evenly. Top with the reserved streusel and remaining apples, allowing them to intermingle slightly. Bake for 65-75 minutes until a tester inserted in the center comes out clean. Once baked, cool the cake in the pan on a wire rack. Then, lifting it by the parchment overhang, transfer to a cutting board, dust with powdered sugar, and slice into 12 servings if serving immediately.

   Do Ahead: The cake can be made 5 days in advance and stored tightly wrapped at room temperature.