• Preheat the oven to 350 degrees F. Grease and flour two 8-inch round pans.

For the Cake:

• Cream the butter and sugar together until smooth, and beat in the eggs one at a time. Stir in the vanilla. Add the flour, baking powder, and salt along with the milk, lemon juice and lemon zest, mixing until just combined.
• Pour the batter equally into prepared pans, and bake for 35-40 minutes. After the cakes cool for 10 minutes, turn them over onto a wire rack to finish cooling.

For the Filling:

• In a small bowl, beat egg yolks until smooth. As the eggs are beating, put a saucepan on medium heat and add the lemon zest, lemon juice and cornstarch. Then, add the butter and sugar to the lemon mixture. Bring the mixture to a boil, and stir for 1 minute. 
• Add a small part of the lemon mixture to the egg yolks, still beating the eggs to make sure they don't cook. 
• Take the saucepan off the heat and stir the egg mixture into the lemon mixture. Stir constantly. 
• Once incorporated, put the saucepan on low heat and stir for 5 minutes or as the mixture thickens. Do not let the mixture boil.
• Pour the mixture into a medium bowl, cover with plastic wrap and store in the fridge. This should be refrigerated for at least 1 hour, up to 3 hours.

For the Frosting:

• In a large bowl, beat the butter together and slowly add the confectioners' sugar. Add the lemon juice and the lemon zest as the confectioners' sugar is added. Add in milk as needed and beat until light and fluffy.

To Assemble:

• Spread the cooled lemon filling onto one cake, and then carefully place the second lemon cake on top. Using a straight spatula, add the frosting in a thin base layer around the cake, then add a final layer on top. You can add as little or as much frosting as you want. To decorate, use leftover icing to pipe flowers on the top using tip 1M. Add lemon zest or lemon peel to garnish the top. Store at room temperature for up to 24 hours, or store in an airtight container in the fridge.