For the Crumb Topping:

3/4 cup flour
3/4 cup firmly packed dark brown sugar
1/2 teas salt
3/4 cup pecans, toasted
6 tbs unsalted butter, cold, cut into 1″ cubes

For the Chocolate Cinnamon Swirl:

1/2 cup sugar
1 teas dark unsweetened cocoa powder
1 teas cinnamon

For the Sour Cream Cake:

3 1/2 cups flour
1 teas baking powder
1 1/2 teas baking soda
1/2 teas salt
1 cup (2 sticks) unsalted butter, soft but cool, cut into 1″ pieces
2 1/4 cups sugar
4 large eggs
16 oz sour cream
1 1/2 teas pure vanilla extract