Christmas Peanut Butter M&M Cookies

0 Preheat your oven to 350°F. Line two baking sheets with parchment paper or silicone baking mats and set aside.  
1 In a large mixing bowl, use a hand or stand mixer to cream together the softened butter, peanut butter, granulated sugar, and brown sugar until light and fluffy (about 2-3 minutes). 
2 Mix in the egg, egg yolk, and vanilla extract, ensuring the mixture is smooth and well-combined.  
3 In a separate bowl, whisk together the flour, baking soda, baking powder, and salt.  
4 Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix.  
5 Gently fold in the M&Ms and chocolate chips (if using).  
6 Scoop about 1.5 tablespoons of dough (a medium cookie scoop works perfectly) and roll into balls and press down slightly. Place them onto the prepared baking sheets, leaving about 2 inches between each cookie. For a bakery-style look, press a few extra M&Ms on top of each ball of dough.  
7 Bake for 9-11 minutes, or until the edges are set but the centers still look slightly soft. Do not overbake – they will continue to firm up as they cool.