Preheat oven to 180C and line 2 baking trays with baking paper.
Add butter and castor sugar to a large bowl and beat with an electric mixer until light and creamy, approximately 3 – 4 minutes.
Add egg and vanilla extract and beat until combined for another 1 – 2 minutes.
In a separate bowl, add the plain flour, baking powder and salt and stir until well combined.
Add the flour mixture to the wet ingredients and mix with a wooden spoon until combined to form a soft dough.
Measure approximately 1 tablespoon of cookie dough, roll into a ball, place on the baking tray and flatten with fingers. Repeat until all dough has been used.
Press some M & M’s gently into the top of the cookie and bake for approximately 11 minutes.
Remove from oven, allow to rest on trays for approximately 5 minutes, then transfer to a wire rack to cool completely.
Store cookies in an air-tight container for up to 3 days. This recipe is suitable to freeze and will make approximately 24 cookies.
Recipe by Mrs Organised at http://www.mrsorganised.com.au/2015/11/19/m-m-christmas-cookies/