Preheat the oven to 350°F (175°C). Grease and flour two 8-inch round cake pans.
In a large bowl, cream 1 cup softened butter and granulated sugar together until light and fluffy, about 3-5 minutes.
Add eggs one at a time, beating well after each addition.
In a separate bowl, whisk together the flour, baking powder, and salt.
Gradually add the dry ingredients to the butter mixture alternately with the milk, beginning and ending with the dry ingredients. Mix until just combined.
Stir in lemon zest, lemon juice, and vanilla extract until evenly incorporated.
Divide the batter evenly between the prepared pans and smooth the tops.
Bake for 35-40 minutes or until a toothpick inserted into the center comes out clean.
Allow cakes to cool in pans for 10 minutes, then turn out onto wire racks to cool completely.
To prepare the lemon buttercream, beat 1 cup softened butter until creamy.
Gradually add powdered sugar, one cup at a time, beating well after each addition.
Add lemon juice and lemon zest, and beat until smooth and fluffy.
If desired, add a few drops of yellow gel food coloring and mix until the color is uniform.
Place one cake layer on a serving plate and spread half of the lemon curd evenly over the top.
Spread a layer of lemon buttercream over the curd.
Place the second cake layer on top and cover the entire cake with the remaining lemon buttercream.
Use a spatula or piping bag to create artistic lemon-themed designs on the cake surface.
Decorate with edible lemon slices or candied lemon peel as desired.
Refrigerate the cake for at least 30 minutes before serving to set the buttercream.