Classic Coffee Cake: A Moist and Delicious Morning Delight

Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round or square cake pan.
Prepare the Cake Batter:

In a large mixing bowl, cream together the softened butter and sugar until light and fluffy. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
Add the Dry Ingredients:

In a separate bowl, whisk together the flour, baking powder, baking soda, and salt. Gradually add the dry ingredients to the butter mixture, alternating with the sour cream, starting and ending with the dry ingredients. Mix until just combined.
Make the Cinnamon Swirl:

In a small bowl, combine the brown sugar and cinnamon. Set aside.
Assemble the Cake:

Pour half of the cake batter into the prepared pan and spread it evenly. Sprinkle half of the cinnamon-sugar mixture over the batter. Add the remaining cake batter on top and spread it out evenly. Sprinkle the rest of the cinnamon-sugar mixture on top.
Prepare the Streusel Topping:

In a small bowl, combine the flour and sugar for the streusel topping. Add the cold, cubed butter and use a pastry cutter or your fingers to work the butter into the dry ingredients until the mixture resembles coarse crumbs. If desired, stir in chopped walnuts or pecans for added crunch.
Add the Streusel Topping:

Sprinkle the streusel topping evenly over the cake batter.
Bake the Cake:

Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.
Serve:

Once cooled, slice and serve your delicious coffee cake. Enjoy it with a cup of coffee or tea for a perfect treat!
Serving and Storage Tips: