01 -
Preheat oven to 350°F (175°C). Grease and flour three 9-inch baking pans, then line the bottoms with parchment paper to prevent sticking.
02 -
Whisk the flour, baking powder, and salt together in a bowl. Set aside.
03 -
Process the sugar with lemon zest in a food processor until the zest is completely incorporated and the sugar becomes moist and pale yellow.
04 -
In a stand mixer, cream the softened butter and lemon sugar together for 3 minutes, scraping down the sides of the bowl as needed.
05 -
Beat in the eggs one at a time, scraping down the bowl between additions. Add the lemon paste if using.
06 -
Reduce mixer to low speed and add the flour mixture just until barely combined, then add the buttermilk and lemon juice. Mix until combined but do not overmix.
07 -
Divide the batter equally between the 3 prepared pans and spread evenly. Bake for 23-25 minutes, until risen and a toothpick inserted in the center comes out clean. Do not overbake.
08 -
Let cakes cool in pans on a wire rack. When completely cool, carefully flip them over and remove the parchment paper.
09 -
Cream the butter and confectioner's sugar, gradually adding enough lemon juice to achieve a spreadable consistency. Add poppy seeds and beat until smooth and creamy. If desired, add a drop of yellow food coloring for a pale yellow tint.
10 -
Stack and frost the cake layers, then garnish with thin lemon slices and fresh mint leaves.