Preheat the oven to 350°F (175°C). Prepare cake pans.
In a large bowl, cream together the butter and sugar until light and fluffy.
Add in the egg yolks and beat until smooth, then mix in buttermilk, lemon juice, and zest.
In another bowl, whisk together flour, baking powder, and salt. Gradually add to the wet mixture.
In a separate bowl, beat the egg whites with cream of tartar until soft peaks form.
Gradually add granulated sugar to egg whites, beating until stiff peaks form.
Fold the whipped egg whites into the cake batter gently.
Divide the batter evenly among the prepared pans and bake for 25–30 minutes.
Let the cakes cool in the pans for 10 minutes before transferring to a wire rack.
Prepare the lemon filling while the cakes cool.
Assemble the cake by layering the cooled cakes with lemon filling between them.
Spread meringue over the top of the assembled cake and swirl decoratively.
Bake the assembled cake for another 10–15 minutes until the meringue is golden brown.
Let the cake cool completely before serving.