Preheat oven to 350 degrees. Line a 13x9 inch pan with aluminum foil or parchment paper.
In a large bowl mix together the flour, baking soda, cornstarch and salt.
In another bowl add sugar, brown sugar and melted butter. Mix well until sugars dissolve in the butter. Add in both eggs and vanilla extract.
Slowly add the flour mixture to the butter mixture while stirring. Once combined add the chocolate eggs reserving a ¼ cup of eggs.
Spread the cookie batter into the baking dish. Press evenly into the corners so you have one smooth layer.
Bake for 30 to 32 minutes or until cookie bar is golden brown and a toothpick inserted in the middle comes out clean. While cookie bar is still warm press the remaining ¼ cup of mini eggs into the top of the bars.
Allow to cool one hour on a wire cooling rack. Use the parchment as handles to carefully lift from pan to cut into square.
Once completely cooled store in an airtight container for 2-3 days.