Preheat your oven to 350 degrees Fahrenheit. Line a cookie sheet with parchment paper and set it aside.

In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until the mixture is light and fluffy. This should take about 2-3 minutes.

Add the egg, egg yolk, and vanilla to the bowl, mixing well until everything is thoroughly combined. Don’t forget to scrape the sides as needed!

In a separate bowl, whisk together the flour, baking soda, baking powder, and salt. Gradually add this dry mixture to the wet ingredients, mixing until just combined.

With a rubber spatula or wooden spoon, fold in 1 cup of M&Ms and the chocolate chips until evenly distributed.

Using a medium-sized cookie scoop, scoop out the dough into balls and place them on the prepared cookie sheet about 1 inch apart. Press the remaining ¼ cup of M&Ms on top of the dough balls to add some extra color.

Bake in your preheated oven for 10-12 minutes, or until the edges are golden. Allow them to cool on a wire rack for about 5 minutes before serving.