Apple Cake

2 sticks unsalted butter
2 cups granulated sugar
3 large eggs
2 teaspoons pure vanilla extract
Grated zest of 1 medium to large lemon
3 cups all-purpose flour
1 teaspoon baking powder
1/2 teaspoon baking soda
Pinch salt
1/2 cup buttermilk
2 large, tart firm apple (about 1 pound), peeled, cored, and cut into1/2-inch dice

Preheat oven to 350 degrees. Butter a 10-inch springform pan. In a large mixing bowl, cream butter and sugar with an electric mixer until light and fluffy. Add eggs, 1 at a time, mixing well after each addition. Add vanilla and grated lemon zest, and mix well. Add 1 1/2 cups of the flour, baking powder, baking soda and salt. Mix until just incorporated. Add buttermilk, and stir well. Add the remaining 1 1/2 cups flour and stir to blend. Add diced apples and stir until blended. Pour batter into prepared pan, spread it to sides of pan with a rubber spatula. Batter will be thick.

Bake until cake is golden brown and toothpick or cake tester inserted in middle of cake comes out clean, 50 to 55 minutes. Let cool.