(adapted from The Weekend Baker by Agibail Johnson Dodge)
300g smooth peanut butter
160g brown sugar
1 large egg
1 tablespoon vanilla extract
60g old-fashioned rolled oats
150g Smarties (mini M&Ms would also work)
Line two baking trays with parchment paper. Preheat the oven to 180°C.
In a large bowl, combine peanut butter and sugar. Beat with an electric mixer on middle speed until well blended. Add the egg and the vanilla extract and mix until well blended. Pour in the flour and mix on low speed until well blended. Add the oats and the Smarties and fold in with a ladle.
Using a small ice-cream scoop or two tablespoons, scoop up rounded tablespoons full of the dough and, using your hands, shape into balls (about 4cm diameter - I made them a bit smaller). Arrange the cookies on the baking trays, leaving about 5cm space between them. Flatten them a little with your hand or a fork.
Bake one tray at a time until the cookies look dry on top, about 12 minutes. Take out of the oven and let cool on the tray for 10 minutes. Then, transfer to a wire rack to cool completely.
Makes about 25 cookies. They can be stored in an airtight container in a cool place for about a week. You can also store them in the freezer for up to 3 months.
If you feel like it, you can decorate them with chocolate glaze after they have cooled down completely. You can use either store-bought glaze, or, over low heat, melt some chocolate (a bit less than 100g should do it) in a small saucepan and, with a teaspoon, drizzle over your cookies.