Preheat the oven to 180°C.
Line the baking tray|trays with some parchment paper or silicon mat.
Sift flour, salt, baking powder and baking soda together.
In a mixing bowl add the sugars and butter.
Beat till the mixture becomes soft and a bit pale.
Add the peanut butter and milk.
Beat till everything is mixed.
Add the flour mixture.
Using a spatula mix till the flour is all wet.
At this point you will know whether you need to add a bit more milk.
If you do, do so 1 tbsp at a time.
Add the mini M&M and mix.
If you find the dough slightly sticky, pop it in the fridge for 20-30 minutes.
If still sticky after that then add 1 tbsp flour.
Take about a lime size of the dough (about 1½ tbsp) and roll into a ball.
Repeat with the remaining dough.
Slightly flatten the balls.
Bake in the preheated oven for 14-16 minutes or till the edges appear golden brown.
Take the trays out of the oven. Let the cookies rest on the tray for 5 minutes as they will be very soft.
Transfer to a wire rack to allow them to cool completely.
Store in an airtight container till required.