Preheat oven to 350°F (175°C) and line two baking sheets with parchment paper.

In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy, approximately 2 minutes.

Add the egg and vanilla extract, beating until fully incorporated.

In a medium bowl, whisk together the flour, baking soda, salt, and cornstarch.

Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined.

Fold in the crushed Mini Eggs and chocolate chips using a spatula.

Scoop rounded tablespoons (approximately 1.5 tablespoons each) of dough onto the prepared baking sheets, spacing them 2 inches apart.

Bake for 10 to 12 minutes, or until the edges are lightly golden but the centers still look slightly soft.

Remove from the oven and let cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.