Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan.
In a mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.
Add the eggs, one at a time, beating well after each addition.
Stir in the sour cream and vanilla extract until well combined.
In a separate bowl, whisk together the flour, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
In a small bowl, combine the chopped nuts (if using), brown sugar, and ground cinnamon.
Spread half of the batter into the prepared cake pan, then sprinkle half of the nut mixture over the batter.
Repeat with the remaining batter and nut mixture.
Use a knife to swirl the batter and nut mixture together gently.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Allow the coffee cake to cool slightly before serving.