Preheat oven to 350°F (175°C) and grease a 4-inch cake pan or 8-oz ramekin. Whisk flour, baking powder, and salt. In another bowl, beat 2 tbsp butter with sugar until creamy, then mix in 2 tbsp beaten egg and vanilla. Stir dry into wet until just combined.

Scrape batter into the pan and bake 18 to 22 minutes until a toothpick comes out clean. Cool in pan 5 minutes, then turn out onto a rack and cool completely, about 20 minutes.

While cake cools, beat 3 tbsp butter until smooth. Mix in powdered sugar a spoonful at a time, then add a drop of green gel coloring and 1 tsp milk. Add more milk a few drops at a time until spreadable.

Spread the green frosting over the top and sides of the cooled cake with the back of a spoon. Chill 5 minutes if frosting gets too soft.

Press candy eyes onto the front. Cut small triangles from candy melts or fruit leather and stick them in a row along the top as spikes. Add tiny dots of white frosting around the eyes and snout if you like. Serve right away.