Preheat the oven to 350°F (175°C). Grease and flour a 9-inch round cake pan, or line it with parchment paper.

In a large mixing bowl, cream together the butter and sugar until light and fluffy. This will take about 3-4 minutes with an electric mixer.

Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract. In a separate bowl, whisk together the flour, baking powder, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, alternating with the milk. Start and end with the dry ingredients. Mix until just combined.

Fold in the sour cream, which will make the cake extra moist. Pour the batter into the prepared pan and smooth the top with a spatula.

Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.

Remove the cake from the oven and allow it to cool in the pan for 10 minutes before transferring it to a cooling rack.

In a medium mixing bowl, sift the powdered sugar to remove any lumps. Add the softened butter, lemon juice, and lemon zest. Stir until smooth.

Add milk, one teaspoon at a time, until the icing reaches your desired consistency. If you want it thicker, use less milk, and for a runnier icing, use more.

Once the cake is completely cool, spread the lemon icing generously over the top using a spatula.