Preheat oven to 350 F. Line two baking sheets with parchment paper.

In a ziplock bag, gently smash the Mini Cadbury Eggs with a rolling pin or a meat mallet. I like to hit them once or twice until they break in half or into thirds. You don't want them pulverized.

In a bowl, sift together flour, cocoa powder, baking powder, and salt. Set aside.

Add 16 ounces (2 3/4 cups) of chocolate chips in a medium-sized microwavable bowl. Microwave on 50% power for two minutes. Stir, then microwave on 50% power for 30 second increments, stirring after each increment, until chocolate is smooth and melted. Toward the end of the microwaving, you'll probably find that a few of the chocolate chips haven't melted, but if you keep stirring, they will melt. Be careful not to overheat the chocolate. 

Mix together eggs and vanilla in a small bowl and set aside. 

In the bowl of a stand mixer or using a hand mixer, cream the butter for 30 seconds on medium speed until fluffy. Add sugars and beat for an additional minute, scraping down sides as necessary. Lower speed and slowly add egg and vanilla mixture, continuing to scrape down the sides and bottom to make sure everything is evenly incorporated. Slowly add the melted chocolate and mix until combined.

Add the dry ingredients to the mixture and mix until just combined. The mixture will probably be really thick at this point, and that's just fine. Add crushed Cadbury Eggs and remaining 1/2 cup chocolate chips and mix until evenly distributed. 

The mixture should be fudge-like. If it's not, let it set for 15-20 minutes until it is more set. Scoop dough with a cookie scoop (I used size 30) and give them quick roll between your hands to smooth them out. Bake for 10-11 minutes. Cookies will still look soft in the middle (be careful not to overbake!) Let cool on sheet pan for five minutes. While they're cooling, garnish with additional Mini Eggs and sprinkles, if desired. Remove to a cooling rack to finish cooling. Enjoy!