Preheat the oven to 350° Fahrenheit. Cover a 13x18 inch baking sheet with parchment paper.
Making The Batter
Use a stand mixer (fitted with the whisk attachment) or hand mixer and beat the butter and sugar on medium-high speed for about 5 minutes. Intermittently use a rubbber spatula to scrape the sides of the mixing bowl.
Add the zest of 3 lemons and the juice of 1 lemon to the batter.
Reduce the speed of the mixer to medium speed and one-by-one add the eggs to the batter. Once the eggs have been fully incorporated, add the flour, baking powder, and the dash of salt to the batter. Continue to beat on medium speed until the batter is thick and creamy.
Spoon the batter onto the prepared baking sheet spread it evenly. and bake the cake for 20 minutes. Once the cake has been baked, insert a wooden toothpick to check for doneness.
Allow the cake to cool completely. While the cake is cooling, use the toothpick to poke several small holes into the cake (this will allow the glaze to seep through and make the cake extra moist).
Glazing The Cake
To make the glaze, use a medium mixing bowl and combine the juice of one lemon (about 3 tablespoons) and two cups of powdered sugar. Use a whisk and mix until the glaze has a creamy consisteny. If the glaze is too thin, simply increase the amount of powdered sugar.
Spoon the glaze onto the sheet cake and use a knife or icing spatula to spread the glaze evenly across the cake. Allow the glaze to harden before serving.
The size of the slices is up to your own preference. I will often cut this cake into smaller slices which results in about 48 slices. This is often beneficial if the cake is intended for a dessert buffet.