Instructions

• Preheat oven to 350°F (180°C). Spray an 8-inch square baking pan with baking spray with flour. Line the pan with parchment paper, leaving an overhang on two opposite sides to use as handles.
• In a medium bowl, whisk together 1 3/4 cups (219 g) all-purpose flour, 1 1/2 teaspoons (7.5 g) baking powder, 1 teaspoon (2 g) ground cinnamon, and 3/4 teaspoon (2.25 g) kosher salt.
• Add 1 1/2 cups (174 g) of the diced Honeycrisp apples to the flour mixture and toss to coat the apple pieces evenly. Set this coated-apple flour mixture aside.
• In another medium bowl, whisk together 1 cup (220 g) firmly packed light brown sugar, 1 large egg (50 g), and 1 large egg white (30 g) until the mixture is lighter in color and slightly fluffy, about 2 minutes.
• Whisk in 1/2 cup (113 g) melted unsalted butter (slightly cooled), 80 g sour cream, 80 g unsweetened applesauce, 1 tablespoon (15 g) fresh lemon juice, and 1 teaspoon (4 g) vanilla extract into the sugar–egg mixture until well combined.
• Using a rubber spatula, fold the flour–apple mixture into the wet ingredients until just combined and no dry streaks remain. The batter will not be completely smooth; stop folding as soon as it is evenly combined.
• Pour the batter into the prepared pan and smooth the top with the spatula. Evenly scatter the remaining 1/2 cup (58 g) diced apples over the batter and gently press them into the surface.
• Bake in the center of the preheated oven for 40 to 45 minutes, or until the top is golden brown and a wooden pick inserted into the center comes out clean.
• Remove the cake from the oven and let it cool in the pan on a wire rack for 10 minutes.
• Use the parchment overhang to lift the cake from the pan and transfer it to the wire rack. Let the cake cool an additional 10 minutes so it is warm but not piping hot before glazing.
• In a small bowl, whisk together 1 cup (120 g) confectioners’ sugar and 2 tablespoons plus 2 teaspoons (40 g) whole milk until smooth and pourable.
• Drizzle the glaze over the warm cake, let the glaze set for a few minutes, then slice and serve. Store leftovers in an airtight container for up to 3 days.