Preheat the oven to 350℉ (180℃). Lightly grease a 9-inch pie plate, or 9-inch round springform pan.
In a large bowl, cream together the butter, brown sugar and granulated sugar until fluffy.
Beat the egg, additional egg yolk and vanilla extract into the butter mixture. Be sure to turn off the mixer and scrape down the sides and bottom of the bowl a few times to ensure that no butter is stuck.
Add in the flour, baking soda and salt. Starting with the mixer on a low speed, gradually mix them into the butter mixture until incorporated.
Stir in the Mini Eggs and chocolate chips.
Press the dough into the pan so that it forms an even layer.
Bake in the middle of the preheated oven for about 25-30 minutes, or until the top looks set and is starting to turn golden brown. The bake time will also depend on how gooey or chewy you prefer your cookie cake. A shorter bake time will lead to a gooier cake.
Remove from the oven and cool the cookie cake in the pan. Optionally, press a few extra Mini Eggs on top of the cookie cake. Be sure to do this while the cake is warm form the oven.