Preheat oven to 350°F (180°C) and line 2 baking sheets with parchment paper.
In a large mixing bowl or stand mixer, beat butter and sugars until pale in color, light and fluffy.
Add egg and vanilla until just combined.
Gradually add flour, baking soda and salt until just combined. If needed, use your hands to press dough together.
Crush half of the Cadbury Mini Eggs and fold into the dough, reserving the remainder to press on top just before baking.
Roll dough into 12 equal dough balls. Drop 6 per sheet, spaced evenly.
Press three mini eggs on top of each cookie.
Bake 9-10 minutes, rotating pans halfway through, until the edges are slightly golden in color. Allow to cool completely before transferring.