• Preheat oven to 350 degrees Fahrenheit. Spray two 9-inch round baking pans with non-stick cooking spray.
• In a medium bowl, mix the 2 ½ cups all-purpose flour, 1 teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon salt, and 5 teaspoons ground cinnamon. Set aside.
• In a large bowl, using an electric or stand mixer on medium speed, beat 4 large eggs and 2 cups granulated sugar for about 2 minutes, or until light and creamy.
• Add the 1 cup softened unsalted butter and 3 teaspoons vanilla extract and beat on low speed for about 1 minute or until well blended. mix in the dry ingredients on low speed until they come together but do not overmix! Add the 1 cup sour cream and beat until smooth.
• Divide the batter evenly into prepared baking pans. Bake for 30 to 35 minutes or until a toothpick inserted in the center comes out clean. Allow the cake to cool before frosting.

Cinnamon Buttercream Frosting:

• Mix 1 cup softened unsalted butter on medium speed with an electric or stand mixer. Beat for 30 seconds until smooth and creamy.
• Add 5 cups powdered sugar, 2 tablespoons milk, 1 teaspoon ground cinnamon, and 1 teaspoon vanilla extract. Increase to high speed and beat for 3 minutes or until smooth.
• Spread the frosting between layers and over the top and sides of the cake. Sprinkle with 1 tablespoon cinnamon-sugar,