In a large bowl, whisk together the flour, cocoa, baking powder, baking soda and salt. If the cocoa is lumpy - be sure to whisk it first.
In a separate large bowl, cream together the butter, brown sugar and granulated sugar until fluffy (about 2-3 minutes, depending on how softened your butter is).
Beat the eggs and vanilla extract into the butter mixture.
Starting with the mixer on a low speed, beat the dry ingredients into the butter mixture. I typically do this about ½ at a time. Turn off the mixer and scrape down the sides and bottom of the bowl to ensure that there are no lumps of butter stuck. The dough will be thick.
Chop ½ of the Mini Eggs. You can also add them to a freezer bag and crush with a rolling pin. They don't need to fine pieces, just chopped in half or in quarters.
Mix the Mini Eggs and chocolate chips into the dough.
Cover the bowl and refrigerate for at least 3 hours or up to 48 hours.
When ready to bake, preheat the oven to 375℉ (190℃). Line baking sheets with parchment paper or silicone baking mats.
Form the cookie dough into balls with about ¼ to ⅓ cup of dough each - mine weighed about 3½ ounces (100 grams) each and I typically get 13-14 very large cookies. Place cookies at least 2½ inches (about 6 cm) apart on the lined cookie sheets.
Bake 1 sheet at a time, for about 12-14 minutes, or until the tops look just set.
Remove from the oven.
For perfectly round cookies, take a large biscuit cutter (larger than the cookies in size) or mug/cup. Place it around the warm cookie (still on the cookie sheet). Gently trace a circular shape to mold the cookie into a perfect circle. Note - you aren't cutting the cookie into a circle, you're simply using the circular shape to gently press the cookies into a perfect circle.
Optionally, press a few extra chopped Mini Eggs into the top of each cookie. Cool the cookies on the pan.