Preheat oven to 350F (175C) and lightly grease and flour a 9" springform pan.
Combine melted butter and sugars in a large bowl and stir until well-combined
¾ cup butter, ½ cup sugar, ¼ cup light brown sugar
Add eggs and vanilla extract, stir well
2 large eggs, 1 ½ teaspoon vanilla extract
Stir in sour cream.
½ cup sour cream
In a separate, medium-sized bowl, whisk together flour, cinnamon, baking powder, baking soda, and salt.
1 ¼ cups all-purpose flour, 1 teaspoon ground cinnamon, ¾ teaspoon baking powder, ¾ teaspoon baking soda, ½ teaspoon salt
Using a spatula, gradually add dry ingredients and wet and stir until just combined-- do not over-mix!
Fold in apple pieces and pour batter evenly into prepared pan. Set aside and prepare your streusel.
1 ½ cups diced, peeled apples
Streusel
Prepare the crumble by whisking together flour, sugars and cinnamon.
1 cup all-purpose flour, ¾ cup light brown sugar, 2 Tablespoons sugar, 1 ½ teaspoon ground cinnamon
Pour the melted butter into the mixture and, using a fork, stir until crumbles form. Evenly sprinkle streusel over batter.
6 Tablespoons butter
Transfer pan to oven and bake on 350F (175C) for 35-40 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool before adding vanilla glaze.
Vanilla Glaze
If desired, make glaze by whisking together powdered sugar, milk, and vanilla. Start with 2 teaspoons of milk and add a third if it isn't thin enough to drizzle.
½ cup powdered sugar, 2-3 teaspoons milk, ¼ teaspoon vanilla extract
Drizzle over cooled cake. Allow glaze to harden, slice, and enjoy!