Preheat the oven to 350℉/180℃. Line two baking trays with parchment paper and set aside. Melt the butter and allow it to cool for 15 minutes before using. Chop the mini eggs and set aside.
1/2 cup mini eggs, 3/4 cups + 2 tbsp unsalted butter
In a bowl, add the flour, cocoa, baking soda, baking powder, cornstarch, cinnamon, and salt. Stir to combine and set aside.
1 2/3 cups all-purpose flour, 1/3 cup unsweetened cocoa powder, 1 tbsp cornstarch, 1 tsp baking soda, 1/4 tsp baking powder, 1/4 tsp cinnamon, 1/4 tsp salt
In another bowl, whisk together the butter, brown sugar, and white sugar until well combined (1-2 minutes)
3/4 cups + 2 tbsp unsalted butter, 2/3 cups dark brown sugar, 1/3 cup white sugar
Add in the egg, egg yolk, and vanilla and continue whisking, scraping the bowl as needed.
1 large egg, 1 large egg yolk, 1 tbsp vanilla
Add in the dry ingredients. Gently fold together with a spatula until just combined - don't over-mix!
Add in the chocolate chips and chopped mini eggs. Mix a few times until evenly incorporated.
1/2 cup semi-sweet chocolate chips, 1/2 cup mini eggs
Scoop the cookies onto a cookie tray (I scooped 6 per tray and used a 2 tbsp cookie scooper), spacing them evenly apart from one another. Add extra chocolate chips and mini eggs on top if desired.
Bake for 13-16 minutes. The cookies are ready when the edges are set to the touch and the middle is slightly puffy. Allow to cool for a few minutes on the hot pan (they will continue to bake as they cool), and enjoy!