Preheat your oven to 350°F (175°C). Grease and flour two 8-by-2-inch round cake pans.

In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and lemon zest.

In a large mixing bowl, cream together the butter and sugar until light and fluffy, about 3-5 minutes.

Gradually add the eggs and yolks, mixing each until fully combined, then add the lemon juice.

Alternately add the flour mixture and buttermilk to the butter mixture, starting and ending with flour.

Evenly divide the batter between the prepared pans and bake for 30-35 minutes or until a toothpick comes out clean.

Cool the cakes in the pans for 10 minutes, then transfer to a wire rack to cool completely.

Cream together the confectioners' sugar and butter for the buttercream, then mix in lime juice, zest, and milk.

Frost between the layers with lime buttercream, and then frost the top and sides of the cake.

Garnish with lime zest or lemon slices if desired before serving.