Preheat oven to 350˚F.
streusel: In a small mixing bowl toss together sugar and flour. Cut in butter until the mixture resembles a coarse sand texture. Set aside.
sour cream cake: In a large mixing bowl, whisk together flour, baking powder, cinnamon, baking soda, salt, and nutmeg. Set aside.
In another mixing bowl or using a stand mixer, cream together butter and sugars. Add eggs, one at a time, scraping down the sides of the bowl once all eggs have been added. Stir in sour cream and vanilla extract and mix until just combined.Stir the flour mixture into the sour cream mixture and stir together until the batter just comes together.
Pour batter into a lightly greased cake pan or springform pan and top with streusel.
Bake crumb cake for 45 to 55 minutes or until a toothpick comes out clean when inserted into the center of the cake.
Allow the crumb cake to cool for about 30 minutes before removing from the cake pan. Slice and serve.