Preheat oven to 350F. Grease a 9x5 inch loaf pan with butter. Add a piece of parchment paper lengthwise to help with removing the cake after baking.
In a medium mixing bowl, combine the flour, baking powder, zest, and salt.
Using a stand mixer, cream together the butter and sugar until fluffy.
Add the eggs one at a time, mixing on a low speed with the paddle attachment. Turn the speed up to medium/high and add in the vanilla and lemon juice.
Put the mixer back on low and add about ½ of the flour mixture. Then half the buttermilk. Repeat until all of the flour and buttermilk are incorporated.
Pour the batter into the loaf pan. Bake for approximately 50 minutes or until a toothpick comes out clean. Allow to cool while making your lemon curd and meringue.
Prepare the lemon curd. In a heavy bottomed saucepan, melt the butter and lemon juice over high heat. In a separate bowl, whisk the sugar and yolks.
Slowly whisk together the hot lemon mixture into the egg mixture, a little at a time. Place the mixture back into the saucepan, stirring constantly. Allow to thicken for 6-8 minutes.
Pour the lemon curd into a glass bowl and cover with plastic wrap, pressing down to cover the entire top. Chill for 1 hour or until the cake has cooked and cooled.
Prepare the meringue: Using a hand mixer, whisk together the egg whites and sugar in a medium metal bowl. Set over a saucepan of simmering water and whisk constantly until the mixture is warm and the sugar has fully dissolved, 1-2 minutes.
Place the meringue mixture in a stand mixer. Whisk on high until light and fluffy, usually about 2 additional minutes.
Assemble the cake: Slice the baked and cooled cake into three horizontal layers. Trim the sides and top to make 3 even layers.
Place the bottom of the cake on a rimmed baking sheet. Top with a layer of the lemon curd. Repeat with the second layer of cake and curd. Top finally with the top layer of cake.
Using a rubber spatula or offset spatula, cover the entire outside of the cake in meringue. Make peaks or swirls as you go to make it extra pretty.
Broil in the oven or use a small hand held kitchen torch to brown the meringue until golden brown. In the oven this would be just about 1 minute, watching carefully. You can also broil just slightly and then further toast the peaks.
Slice and serve! Enjoy.