In the bowl of a mixer (or a large mixing bowl), cream together the butter and sugars until
light and fluffy, about 3 minutes. Add in the egg, vanilla, and milk. Mix until combined,
scraping down the sides of the bowl as needed. Gradually add in the dry ingredients, until
just moistened. Fold in the chopped mini eggs until evenly distributed throughout the
dough. (Save a few whole mini eggs for later.)