Preheat the oven to 180ºC/160ºfan. Grease and line a 9inch x 9inch cake tin.
In a mixing bowl, cream together the butter and sugar. Use a fork to break up the sugar if it's lumpy before adding to the butter.
Stir in the eggs and vanilla.
Sieve in the flour, salt and bicarb and stir together.
Add the milk and stir together.
Leave a handful of mini eggs for the topping. Chop up the rest of the mini eggs and stir in too.
Spoon the cookie dough into the pan and level out.
Place in the oven and after 5 minutes remove and add the remaining eggs to the top (this keeps some on the top). Bake until golden brown. If you like your cookies slightly gooey take them out at 15 minutes. 18-20 minutes if you want them to be set more.