5 jumbo-sized eggs, separated
1 cup buttermilk
4 sticks butter, plus 1 tablespoon, for pan
3 cups cake flour, plus 2 tablespoons, for pan
1 Granny Smith apple, peeled, cored and diced into 1/8-inch pieces
1/2 teaspoon ground cinnamon
1 teaspoon lemon juice
2 1/2 cups sugar, divided
1 teaspoon vanilla extract
1 teaspoon lemon extract
3 teaspoons baking powder
Special equipment: 10-inch Bundt cake pan
Preheat oven to 325 degrees F. Let the eggs, milk and butter come to room temperature on the counter before beginning. (Butter goes on the counter last.)
Butter the Bundt pan with 1 tablespoon of butter, then add 2 tablespoons of flour and shake and tap to coat the interior of the pan; set aside. Put the diced apples in a bowl with the cinnamon and lemon juice. In a large bowl or stand mixer add the butter and 2 cups of sugar and beat until smooth. Add the egg yolks, 1 at a time, and blend to completely incorporate before adding the next. The mixture will become very light in color. Add the buttermilk and the extracts and mix to combine. Stir in 3 cups of flour along with the baking powder and stir until incorporated.
In a separate clean dry bowl, whisk egg whites until foamy, then add the remaining 1/2 cup of sugar and whisk until shiny and soft peaks form when removing the whisk from the whites. Gently fold this into the cake batter. Pour half of the batter into the prepared pan. Arrange the apples in the center of the ring all the way around, being sure they don't touch the outer or inner edge of the pan. Pour in the remaining batter and bake for 1 hour and 30 minutes. Remove the cake from the oven and cool completely. Put a large plate or cake plate on top of the pan, then holding both together, flip them so that the curved bottom of the Bundt pan is on the top and the plate is resting on a flat surface. Slowly remove the pan from the cake by lifting it straight up. Slice and serve.