• Preheat oven to 350 F. Prepare a 9x13 inch baking dish with cooking spray. If mixing by hand, follow along with instructions in a large mixing bowl. 

  In stand mixer with paddle attachment, cream together ¾ cup butter, ½ cup brown sugar, and ¼ cup granulated white sugar on high speed until fluffy, about 2 minutes.
• Add2 large eggs and 1 teaspoon vanilla and mix well.
• Add 1 cup sour cream (or greek yogurt) and 1½ cups mashed banana (I peel them and put them straight into the mixer, they get mashed as they mix). 
• In separate bowl combine 2¾ cups all purpose flour, 1 teaspoon salt, 2 teaspoons baking powder, and ½ teaspoon baking soda. Pour into the wet mix and mix on low speed until just combined. Do not overmix. 

For Streusel topping:

• In a medium bowl combine 1 cup flour, 1 cup brown sugar, ½ cup butter, softened and 1 Tablespoon cinnamon and mix well. Stir in 1 cup walnuts, chopped. Sprinkle evenly over coffee cake batter.   
• Bake at 350 F for 40-45 minutes or until an inserted toothpick comes out clean. Let cool 15-20 minutes before glazing. 
• In a small bowl or plastic bag, mix together 1 cup powdered sugar,½ teaspoon vanilla, and 1½ Tablespoons milk. Use a spoon (or snip off a tiny corner of the bag) and drizzle glaze over the cake diagonally one direction, then diagonally the other direction like a letter X. 

  Slice and serve. Enjoy!