Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a mixing bowl, combine flour, sugar, baking powder, and salt.

Add softened butter, milk, eggs, lemon zest, and lemon juice. Mix until smooth.

Divide the batter evenly between the prepared cake pans.

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

Let the cakes cool in the pans for 10 minutes, then transfer to a cooling rack to cool completely.

In a mixing bowl, beat the softened butter until creamy.

Gradually add powdered sugar, mixing well after each addition.

Add lemon juice, lemon zest, and vanilla extract. Beat until fluffy.

Once the cakes are completely cooled, place one layer on a serving plate.

Spread a layer of frosting on top, then place the second cake layer on top.

Frost the top and sides of the cake with the remaining frosting.

Decorate with additional lemon zest if desired.