01 - Preheat oven to 350°F. Grease three 8-inch round cake pans and line bottoms with parchment paper.
02 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl. Set aside.
03 - Beat softened butter and granulated sugar in a large bowl until light and fluffy, approximately 3-4 minutes.
04 - Add eggs one at a time, beating thoroughly after each addition. Mix in vanilla and almond extract until combined.
05 - Gradually add flour mixture in three parts, alternating with buttermilk, beginning and ending with flour mixture. Mix until just incorporated.
06 - Add green gel food coloring and mix until batter reaches desired shade of green.
07 - Divide batter evenly among prepared pans. Bake for 25-30 minutes until toothpick inserted into center comes out clean.
08 - Let cakes cool in pans for 10 minutes, then transfer to wire racks to cool completely before frosting.
09 - Beat butter until creamy. Gradually add powdered sugar on low speed. Add milk, vanilla, and salt. Beat on high speed until fluffy and smooth.
10 - Tint a portion of frosting with green food coloring if desired for decorative piping.
11 - Place one cake layer on serving plate. Spread with frosting, top with next layer, and repeat. Frost top and sides evenly.
12 - Finish with green sprinkles or edible shamrock decorations as desired.