Preheat your oven: Set your oven to 350°F (175°C). Grease and line a 6-inch round cake pan with parchment paper.

Mix dry ingredients: In a large mixing bowl, sift together the flour, sugar, cocoa powder (if using), baking powder, baking soda, and salt.

Cream the butter: In another bowl, cream the softened butter until light and fluffy. Add the eggs, one at a time, mixing well after each addition.

Combine wet ingredients: Add the buttermilk and vanilla extract to the butter mixture, mixing until well combined.

Combine mixtures: Gradually add the dry ingredients to the wet mixture, stirring until just combined. Do not overmix.

Bake the cake: Pour the batter into the prepared cake pan. Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.

Cool the cake: Allow the cake to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.