Start by preheating your oven to 375F.
Then line a baking sheet with parchment paper and set aside. You could either line several baking sheets to place them all in the oven at once. Or do one small batch at a time and reuse the parchment each time.
In a large mixing bowl, beat together the sugar, brown sugar and butter together until combined.
Next, add the vanilla and egg. Be sure to scrape down the bowl and mix until combined.
Slowly add the flour, baking soda and salt. Again, scrape down the bowl and mix until everything is combined.
Stir in the chocolate chips and 1 cup of the mini eggs with a wooden spoon or rubber spatula. You can also use your hands for this part, which I found to be easier to get the choc chips and candy evenly dispersed in the dough.
Scoop the dough with a 2 ounce ice cream scoop onto the lined baking sheet.
A 2 ounce scoop is 4 tablespoons, which seems pretty large for cookies. But after testing different sizes, I found that I liked the larger ones the best. They end up a bit softer than a smaller version of these cookies, which I prefer.
With the remaining ¼ cup of mini Cadbury eggs, add them to the top of any cookies that may need to be topped up with extra eggs.
Bake for approximately 10-12 minutes, or until lightly golden brown. For crispier cookies, bake for 13-15 minutes.