Preheat your oven to 350°F. Grease a 9×5-inch loaf pan with a bit of butter. Adding a piece of parchment paper can help with easy removal later.
In a medium mixing bowl, combine the flour, baking powder, lemon zest, and salt. Whisk until well mixed and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and 1 cup of granulated sugar until fluffy, which should take about 2 minutes. You want a light, airy mixture.
Add in the eggs one at a time, mixing well after each addition. Then, turn the mixer speed up to medium-high and mix in the vanilla and lemon juice.
Reduce the mixer speed to low and add half of the flour mixture, followed by half of the buttermilk. Alternate adding the remaining flour and buttermilk until just combined.
Pour the batter into the prepared loaf pan and bake for approximately 50 minutes, or until a toothpick inserted comes out clean. Allow it to cool while you prepare the lemon curd and meringue.
For the lemon curd, melt the butter and fresh lemon juice in a heavy-bottomed saucepan over high heat. In another bowl, whisk the sugar and egg yolks together until well combined.
Slowly whisk the hot lemon mixture into the egg mixture, a little at a time, to avoid cooking the eggs too quickly. Return the mixture to the saucepan and stir constantly for 6 to 8 minutes until it thickens.
Once thickened, pour the curd into a glass bowl and cover with plastic wrap, pressing it directly onto the surface to prevent a skin from forming. Chill in the refrigerator for at least 1 hour.
Now, prepare the meringue. In a clean metal bowl, whisk together the egg whites and 1 cup of sugar over a saucepan of simmering water. Whisk constantly until warm and the sugar has dissolved, about 1 to 2 minutes.
Transfer the meringue mixture to the bowl of a stand mixer fitted with the whisk attachment. Whisk on high speed until light and fluffy, usually about 2 additional minutes.
Once your cake has cooled, slice it into three horizontal layers. Assemble the cake by placing the bottom layer on a rimmed baking sheet, then spreading a layer of lemon curd on top. Repeat this process with the second layer of cake and curd, topping it off with the final layer of cake.
Using a rubber spatula or offset spatula, cover the outside of the cake with meringue, creating peaks and swirls for a beautiful finish.
Broil in the oven or use a kitchen torch to brown the meringue until golden brown, which should take about 1 minute. Keep a close eye on it to avoid burning. Once done, slice and serve your stunning Lemon Meringue Cake!
