Pre heat your oven to 170c
Use a rolling pin to break three quarters of the Mini Eggs into large chocolate chunks. Leave the other quarter whole and set aside.
In a bowl cream together the butter and sugar until pale and fluffy. Next add the vanilla and egg and whisk once more until combined.
Add the salt, bicarbonate of soda and sifted flour. Stir with a wooden spoon until the mixture starts coming together.
Tip in the broken Mini Eggs and mix once more. Now tip onto a clean surface and bring the dough together with your hands until it is smooth and shiny.
Chill the dough for 20-30 minutes. Moulding into a thick sausage shape and wrapping in greaseproof paper will make it easier to handle later.
Remove the chilled dough from the fridge and cut into 16 portions. Shape these into thick disks and place one a lined baking tray, no more than 8 on a tray. Use the remaining whole Mini Eggs to decorate the top of your cookies by adding 2-3 to each cookie surface.
Bake for 15 minutes until light golden brown at the edges but pale in the centre.