• Preheat the oven to 350 degrees F. Grease and flour a 9x9 square pan or round pan (pie dish).

For the Cake:

• Cream the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment for 4 to 5 minutes, until light. Add the eggs 1 at a time, then add the vanilla, butter, and sour cream.
• In a separate bowl, sift together the flour, baking powder, baking soda, and salt.
• With the mixer on low, add the flour mixture to the batter until just combined. Finish stirring with a spatula to be sure the batter is completely mixed. Fold in pecans.

For the Streusel:

• Whisk the flour, sugar, and salt together in a large mixing bowl until combined. Cut in the butter in very small pieces. If you don't have a pastry cutter (I don't), you can use your hands or mix with a fork until the mixture resembles coarse crumbs.
• Work the brown sugar and cinnamon into the flour mixture, or squeeze the mixture with your hands, almost like playdough, for 3-5 minutes. I prefer to use my hands. You want the mixture to look like one big brown sugar clump, thats how you get the larger crumbs. Break the large crumb into chunks and sprinkle over the batter, pressingly lightly so they stick. Bake the cake until the center is firm and a toothpick inserted in the center comes out clean, about 30-35 minutes.
• Allow to cool completely before serving, about 2 hours.