In a large mixing bowl, mix peanut butter, brown sugar, egg, baking soda and vanilla until well combined. Stir in chocolate chips.
Use a small cookie scoop, drop rounds 2 inches apart onto baking sheets lined with parchment paper. Use the bottom of a glass dipped in sugar to flatten the cookies slightly. Press several M&M’s in to the top of the cookies.
Bake the cookies for 12 to 14 minutes until the tops are crinkled and before the edges begin to brown. Cool on sheets 5 minutes. Transfer to racks; cool completely before serving.