Preheat oven to 325 degrees and spray a donut pan lightly with cooking spray.
In a large bowl, whisk together flour, cocoa powder, baking powder, salt, and both sugars.
In a separate small bowl, whisk eggs with milk, vanilla, and melted butter.
Gently stir wet ingredients into the dry ingredients until just combined, taking care not to over-mix. Fold in crushed ½ cup Cadbury Mini Eggs.
Fill each cavity of prepared donut pan almost all the way with batter. Bake for 9-11 minutes, until doughnuts are light and springy to the touch. Let cool in pan for a couple minutes before removing to baking rack to cool completely. Repeat with additional batter.
Dunk donuts upside-down into icing and then place back on rack and top with the remaining crushed Cadbury Mini Eggs. Let donuts rest for about 30 minutes so icing can harden.