Start by thinly slicing 2 apples into half-moon shapes. Peel and coarsely dice the remaining apple.
Lightly grease and line a 9-inch springform pan with parchment paper; preheat the oven to 395-400°F.
In a small bowl, drizzle 1 tbsp of lemon juice over the diced apple and coat it with 1 tbsp of sugar.
Using a stand or hand mixer, beat egg whites until soft peaks form. Set aside.
In another small bowl, whisk together flour, baking powder, and sugar.
In a large bowl, whisk together milk, eggs, cooled melted butter, and lemon zest. Gradually add the flour mixture, incorporating it 1/3 at a time. Mix until there are no visible streaks of flour.
Gently fold in the beaten egg whites and ½ cup of apples cut into ½“ cubes.
Pour the batter into the prepared pan and bake for 30-40 minutes.
Allow the cake to cool before removing it from the pan. Dust with powdered sugar before serving.
