Preheat the oven to 350°F (175°C) and prepare cake pans.
Whisk together dry ingredients: flour, sugar, baking powder, and salt.
Cream together softened butter and sugar until light and fluffy.
Add in egg yolks one at a time, mixing well after each addition.
Mix in milk and lemon zest until smooth.
In a separate bowl, beat egg whites until soft peaks form, adding cream of tartar.
Gradually add sugar to egg whites, beating until stiff peaks form.
Gradually fold the egg whites into the cake batter.
Divide the batter among the prepared cake pans and bake for 25-30 minutes.
Prepare lemon curd while the cakes are baking.
Beat egg yolks with sugar, lemon juice, and cornstarch over a double boiler until thick.
Once thickened, remove from heat and stir in butter until melted.
After cakes have cooled, layer them with lemon curd in between.
Spread meringue over the top layer of the cake and toast with a kitchen torch.
