Preheat the oven to 350°F. Prepare a 9x9 metal baking dish. Butter and line with parchment paper.
In a large mixing bowl, combine the softened butter, brown sugar, and granulated sugar.
Add the eggs, vanilla extract, baking powder, baking soda, and salt and combine.
Add the flour and combine.
Add the chocolate chips and half to two-thirds of the mini eggs. Use a large mixing spoon to combine. Do not use a hand-held or stand mixer at this stage, which will break the eggs unnecessarily. Reserve the remaining mini eggs to decorate the top.
Press the cookie batter into the prepared baking dish. Use the remaining Cadbury Mini Eggs to decorate the top of the cookie bars.
Bake for 20-25 minutes until the edges start to lightly brown. Allow to cool fully in the baking dish. Then use the overhanging parchment paper to lift the bars out of the dish and place it on a cutting board. Cut into 25 equal squares.
Notes
Mini Eggs vs. Chocolate Chips: If you don't mind buying another bag of Cadbury Mini Eggs or if you don't already have chocolate chips, you can substitute some or all of the chocolate chips with additional mini eggs.Adding the Mini Cadbury Eggs: When mixing in the Mini Cadbury Eggs, use a large mixing spoon. Avoid using a hand or stand mixer at this stage to avoid cracking the eggs.Choosing a Baking Dish: This recipe calls for a metal 9x9 baking dish for thick Mini Egg Bars. If you do not have a 9x9 dish you can use these other options and adjust the baking time:
8x8 baking dish: Add 5-10 minutes to the baking time.
9x13 baking dish: Reduce the time by to up 10 minutes. Start checking at the 15-minute mark.
9x9 ceramic dish: Add 5-10 minutes to the baking time.
Preparing the Dish: Butter the 9x9 baking dish. Then line the dish with parchment paper. Trim the parchment paper with scissors if needed. The butter helps the parchment paper stick to the pan.Pressing the Bars into the Baking Dish: This is a thick dough. In order to press it evenly into the baking dish you can either put your hand inside a plastic baggie or use an extra piece of parchment paper to push the dough into the corners of the dish for an even layer of dough that stretches all the way to the corners of the dish.Decorating the Mini Egg Bars: Reserve one-half to one-third of the eggs to sprinkle on top of the dough pressed into the baking dish at the end to decorate.When the Mini Egg Bars are Done: The Mini Egg Bars are done when the edges start to brown, but the middle has not fully browned yet. This may be difficult to tell while the bars are still in the oven, so keep a close eye on it, and when they look close to done slide them out of the oven slightly and check in the light of the kitchen.Eggs Cracking: The eggs will crack when baked, that’s okay. You’ll need to cut into the bars which will cause cracks anyway, so cracking while baking is not a big deal. You can add additional eggs to the top after the bars come out of the oven, but because the dough has already been baked and formed a crust, it will not look as nice.