• Preheat the oven to 350 degrees Fahrenheit and spray an 8-inch or 9-inch round cake pan with 2-inch high sides with pan spray. You may add a parchment round to the bottom of the pan and spray it with pan spray, but that is optional. Mix ⅓ cup granulated sugar and 1 tablespoon ground cinnamon evenly in a small bowl. Set aside.

Streusel Topping

• Add ⅔ cup all-purpose flour, ¼ cup granulated sugar, ¼ cup packed brown sugar, 1 teaspoon ground cinnamon, and ¼ teaspoon salt to a medium bowl and whisk to combine.
• Add the cold 6 tablespoons unsalted butter and use a pastry cutter to cut it into the flour mixture until the butter is the size of small peas. You may also use clean hands to rub the butter into the mixture by rubbing it between your fingers. Just be careful not to completely rub all the butter into the flour. Cover the bowl and set it in the refrigerator while you prepare the cake batter.

Cake

• Add ½ cup unsalted butter, 8 ounces sour cream, ½ cup granulated sugar, ⅓ cup packed brown sugar, 2 large eggs, and 2 teaspoons vanilla extract to a large bowl and whisk until smooth and combined.
• Whisk together 1 ½ cups all-purpose flour, 1 teaspoon baking powder, ½ teaspoon salt, and ½ teaspoon baking soda in a separate bowl.
• Add the flour mixture to the sugar mixture and mix until combined.
• Add half of the cake batter to the prepared cake pan. Top it with the cinnamon sugar mixture.
• Add the rest of the cake batter on top of the cinnamon sugar and spread until smooth and even before distributing the streusel evenly over the top of the cake batter.
• Bake for 40-45 minutes, or until a toothpick comes out mostly clean from the center of the cake. Let the coffee cake cool completely before carefully turning it out of the baking pan. Slice into pieces and serve.