Adapted from Ina Garten
1 stick butter (1/2 cup), at room temperature
1/2 cup dark brown sugar
1/2 cup sugar
1 egg, at room temperature
1 teaspoon vanilla
3/4 cup flour
1/2 teaspoon baking powder
1/4 teaspoon salt
1 1/2 cups old-fashioned oatmeal
1 cup mini M and M's, reserve some to garnish tops
Preheat the oven to 350º. Line baking sheets with parchment paper.
Cream butter, brown sugar and sugar till thoroughly mixed. Add eggs, then vanilla and mix well. Add flour, baking powder, and salt, and mix till all flour is incorporated. Mix in oatmeal, then M and M's. Cover and chill dough at least an hour.
Scoop out tablespoons of dough and place on prepared baking sheets, about 2 inches apart. Press a few of the reserved M and M's into dough balls. Bake 12-14 minutes. Cool for a couple minutes on pan, then remove to wire rack to finish cooling.