Preheat oven to 375 degrees.
Melt ½ cup butter for brownie cups. Add to sugar, eggs, and vanilla. Stir with wooden spoon.
In a separate bowl, combine flour, cocoa powder, salt, and baking powder until combined. Stir into wet ingredients with wooden spoon just until mixed. Do not beat or overmix.
Scoop 2 teaspoon size amounts into a greased mini muffin pan (with each cavity about halfway full).
Bake for 15-18 minutes or until releasing from edges and a toothpick inserted in middle comes out clean.
Let cool and use back of a wooden spoon to push down brownie center for gold. Pour in gold sprinkles.
In a mixing bowl with paddle attachment, beat together butter and 2 cups powdered sugar. Add additional sugar 1 cup at a time. Add cream (or milk) and food coloring. Beat for 2-3 minutes on medium until light and fluffy.
Using a piping bag and fluted tip, swirl on a dollop of frosting to each brownie cup to hide the gold surprise! Top with a shamrock decoration or sprinkles.