Cream the butter and sugars

• Beat the softened butter with the brown sugar and granulated sugar until light and fluffy.
• Beat in the egg and vanilla extract until smooth.

Make the cookie dough

• Whisk the flour, baking soda and salt together.
• Add the dry ingredients to the butter mixture and mix until just combined.
• Fold in the M&M's.

Chill the dough

• Cover the dough and refrigerate so the cookies spread less.

Shape the cookies

• Preheat the oven to 180 °C.
• Roll the dough into balls and place them on a lined baking tray, spacing them apart.
• Press a few extra M&M's on top of each ball.

Bake

• Bake until the edges are golden and the centers still soft.

Cool

• Let the cookies rest on the tray for a few minutes, then transfer to a cooling rack.