Step 1

For the streusel: Mix together the sugars, salt, cinnamon and pecans, if using, in a small bowl.

Step 2

For the cake: Preheat the oven to 325 degrees. Generously grease a 10-inch Bundt pan with cooking oil spray.

Step 3

Combine the butter and granulated sugar in the bowl of a stand mixer or handheld electric mixer; beat on medium speed for several minutes, until light and fluffy. Add the eggs one at a time, beating well after each addition. Stop to scrape down the bowl.

Step 4

Sift together the flour, baking soda, baking powder and salt on a large sheet of wax paper or in a bowl. On low speed, add the flour mixture alternately with the sour cream or crème fraiche, ending with the dry ingredients, to form a very thick batter. Stir in the vanilla extract.

Step 5

Pour half the streusel into the bottom of the Bundt pan, distributing it evenly; this will give the cake a caramelized appearance. Spread half the batter in the pan evenly, then scatter the remaining streusel on top of the batter layer. Top with the remaining batter, making sure to cover the streusel layer completely.

Step 6

Bake (middle rack) for 50 minutes, or until a tester inserted into the cake comes out clean (except for maybe a few streusel crumbs). Let cool completely before inverting onto a platter.