Preheat oven to 350F. Move the rack to the middle position.

Melt the butter in a large, microwave-safe bowl. Let it cool for a few minutes while you prepare/measure out the rest of the ingredients and line an 8x8 baking dish with tin foil (and/or spray it with non-stick spray).

Add the egg, vanilla, and sugar to the bowl and stir until it's combined, then stir in the baking powder and flour until smooth. Try not to over stir.

Stir in the white chocolate chips and Mini Eggs. Transfer batter to the baking dish and smooth it out.

Bake for 30 minutes, or until a toothpick comes out (mostly) clean. You don't want gobs of raw batter stuck on it, basically. Let cool in the baking dish for at least 30 minutes. Cut into squares and enjoy.