Preheat oven to 350°. Melt butter in a microwave-safe dish for 40 seconds.
Beat butter with sugars until creamy; add vanilla and egg. Beat on low for 10 to 15 seconds; avoid overbeating as it will lead to stiff cookies.
In a separate dish, mix flour, baking soda and salt until combined. Slowly add to the wet ingredients until crumbles form.
Add crushed Cadbury eggs, setting aside 1/4 cup.
Roll dough into 9 to 12 large balls and place on a lined baking sheet. Top each ball of dough with the a spoonful of the remaining Cadbury eggs and lightly push into the dough before setting into the oven.
Bake cookies for 9 to 12 minutes until puffy and golden. Let cool for 30 minutes and enjoy!
Notes
These cookies freeze well. Feel free to make an extra batch or two to freeze and enjoy all season long.