Preheat the oven to 350 degrees. Line a baking sheet with parchment paper.

Combine butter, brown sugar, and granulated sugar in a stand mixer and beat until light and creamy.

Add the egg and vanilla extract; beat until smooth.

Gradually add flour, baking soda, salt, and oats; mix until combined.

Stir in chocolate chips and 1 cup of crushed Cadbury mini eggs with a spoon.

Scoop dough onto the prepared baking sheet using a 3 tablespoon scoop, spacing 3 inches apart.

Bake for 8 to 9 minutes until edges are golden brown.

Top the cookies with remaining crushed Cadbury eggs.

Cool on the pan for about 10 minutes before transferring to wire racks to cool completely.