Instructions

1. Preheat the oven to 350°F and line the bottom of a 9-inch round cake pan with parchment paper and grease the sides. Set aside.
2. First, make the cake. In a stand mixer fit with the paddle attachment, beat the butter and granulated  sugar together on medium speed until light and fluffy, about 2 minutes.
3. Turn off the mixer, then add the eggs one at a time and beat at low speed, scraping down the bowl between each addition. Add the vanilla extract and mix.
4. In a separate bowl, whisk together the flour, baking powder, baking soda, and salt. With the mixer on low speed, alternate adding in the dry ingredients and the sour cream in 3 additions (you’ll add half the dry, then all of the sour cream, then the other half of the dry). It’s okay if the batter still has a few lumps in it–you don’t want to overmix.
5. Transfer half the  batter to the prepared pan, using a silicone spatula to spread it into an even layer. Set to the side while you make the filling
6. Make the cinnamon apple swirl. In a small bowl combine the apple pieces, brown sugar, and spices. Stir to evenly coat the apples.
7. Top the batter in the pan with the cinnamon apple mixture and spread it all the way to the edges. Spoon the remaining half of the batter over the apples, carefully spreading it onto an even layer. It will seem a little thin, but don’t worry–it will rise! Set aside.
8. Next, make the crumb topping. In a large bowl, add the melted butter, flour, brown sugar, granulated sugar, cinnamon, and salt. Use a fork (or your hands!) to cut the mixture together until the mixture is pebbly. Sprinkle the crumb evenly over the batter.
9. Bake until a butter knife inserted into the middle comes out mostly clean, 38 to 42 minutes. Place the pan on a cooling rack and allow the cake to cool completely in the pan. If desired, dust the top with powdered sugar. Slice and serve!