Created by KittenCal on October 25, 2011
Step 1: For the streusel; combine the brown sugar, flour and cinnamon, then mix in melted butter, then the nuts; set aside.
Step 2: For cake; preheat oven to 350 degrees F (set oven rack to second-lowest position then grease a 9-inch square baking pan.
Step 3: In a mixing bowl using an electric mixer on medium speed beat butter with dark brown sugar, and white sugar until combined.
Step 4: Add eggs one at a time beating until blended after each addition.
Step 5: Add vanilla beating until blended.
Step 6: Add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture; beat at low speed until blended after each addition.
Step 7: Pour batter into pan; sprinkle evenly with the prepared streusel topping.
Step 8: Bake for 35 to 40 minutes or until a wooden pick inserted in center comes out clean.
Step 9: Serve warm or at room temperature.