Preheat the Oven and Prepare the Pan: Preheat the oven to 180°C (350°F). Grease and flour an 8-inch round cake pan, or line it with parchment paper for easy removal.
Mix the Dry Ingredients: In a medium-sized bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, and salt. Set aside.
Cream the Butter and Eggs: In a large bowl, beat the softened butter with an electric mixer on medium speed until light and fluffy. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Combine Wet and Dry Ingredients: Gradually add the dry ingredients to the butter-egg mixture, alternating with the milk and sour cream. Start and end with the dry ingredients. Mix until just combined.
Optional: Add Melted Chocolate: If using melted chocolate, gently fold it into the batter. This step will add extra richness to the cake.
Bake the Cake: Pour the batter into the prepared cake pan and spread it out evenly. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool in the pan for 10 minutes before removing it and transferring to a wire rack to cool completely.
Serve and Enjoy: Once the cake has cooled, slice and enjoy! You can serve it as is or with a dusting of powdered sugar or whipped cream for added indulgence.