Creating Copycat Starbucks Coffee Cake is a straightforward process. Follow these steps for a successful bake:

1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour a 9×13-inch baking pan.
2. Mix Dry Ingredients: In a large bowl, combine 2 cups of all-purpose flour, 1 cup granulated sugar, 1/2 cup packed brown sugar, 1 teaspoon baking powder, 1 teaspoon baking soda, and 1/2 teaspoon salt. Mix thoroughly.
3. Combine Wet Ingredients: In another bowl, whisk together 1 cup of sour cream, 1/2 cup softened butter, 2 large eggs, and 1 tablespoon vanilla extract until well-combined.
4. Combine Mixtures: Gradually add the wet ingredients to the dry ingredients, stirring until just combined. Be careful not to overmix.
5. Add Nuts: If you like, fold in 1/2 cup of chopped walnuts or pecans for added crunch.
6. Prepare Topping: In a separate bowl, mix together 1/2 cup all-purpose flour, 1/2 cup packed brown sugar, 1 teaspoon cinnamon, and 1/4 cup melted butter until crumbly. Stir in 1/2 cup chopped nuts if desired.
7. Layer the Batter: Pour half of the batter into the prepared baking pan, spreading it evenly across the bottom.
8. Add Topping: Sprinkle half of the crumb topping mixture over the batter. Add the remaining batter on top and finish with the rest of the crumb topping.
9. Bake: Place in the preheated oven and bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.
10. Cool: Once baked, remove from the oven and let it cool in the pan for about 15-20 minutes before cutting.