#1 Preheat oven to 375 degrees F. Butter and flour an 8-inch spring-form pan #2 In the bowl of an electric mixer, beat butter and sugar until light and fluffy, about 2 minutes. At low speed, add the eggs, one at a time and vanilla #3 In a separate bowl, mix all the dry ingredients and lemon zest until well combined. Slowly, add the flour mixture and beat at low speed. Scrape the sides of the bowl as needed. Add apple and sour cream. Mix for 1 minute until just combined #4 Scrape the batter into the prepared pan, smooth the top and bake for 25-30 minutes, until the cake is golden brown and toothpick inserted in the center comes out clean #5 Cool in the pan on a wire rack for 10 minutes. Remove the cake from the pan and cool completely #6 Sift powdered sugar over the top.