Preheat oven to 350°F. Soften butter if needed by microwaving for 10 seconds.
Cream together 1 cup softened butter and sugar using a mixer on medium speed for 20-30 seconds.
Add egg, vanilla extract, and almond extract gradually while mixing on medium speed.
Add baking powder, salt, and flour half a cup at a time on low speed, mixing just until combined.
Spray a 9x13 inch pan with cooking spray and line it with parchment paper, leaving a 2 inch overhang.
Drop dough by tablespoon-sized chunks into the pan and press evenly to cover the pan surface.
Bake for 14-16 minutes until edges are slightly browned but centers seem just set.
Cool bars completely before frosting, refrigerate if needed to speed cooling.
For frosting, beat 1/2 cup softened butter on medium speed until creamy.
Slowly add vanilla, almond extract, and powdered sugar while mixing continuously.
Increase mixer speed to high, beat frosting for 2 minutes until fluffy.
Add milk tablespoon by tablespoon to achieve spreadable consistency.
Mix in green food coloring until color is uniform.
Spread frosting over cooled bars, add sprinkles immediately if using.
Chill or freeze bars for 30-60 minutes before cutting to prevent frosting smearing.
Cut into 24 pieces using the recommended tree shapes.
Store bars in an airtight container. They keep well refrigerated or frozen.