Line a baking sheet with parchment paper, and preheat your oven to 350°F
In a small bowl, combine flour, salt and baking soda, whisking together. Set aside
In a medium-large bowl, combine softened butter, granulated sugar and brown sugar. Beat on medium until combined and lighter in color (about 3 minutes)
Add egg and vanilla to butter mixture and beat until homogenous.
Switch to low and add in cocoa powder, and once mixed into the dough add food coloring. I used gel food coloring and approximately ¼-½ tsp. If you are using a regular liquid food coloring you will probably need more. Depending on the brand of food coloring I would start by adding about 4-5 drops, mixing in completely and seeing if you need more.
Add your flour mix to your wet ingredients and mix until just combined.
Add your m&m's and mix in using a rubber spatula or spoon.
Scoop your cookies onto the baking sheet. I used a 2 tbsp cookie scoop. A larger scoop could be used however this will most likely affect bake time and the amount of cookies produced. Leave about 2-3 inches of space between each cookie.
With your sanding sugar in a small bowl, take one cookie dough scoop and roll into a ball between your palms. Place the cookie dough into the sanding sugar and coat. Place back on the baking sheet.
Repeat with the rest of the cookie dough.
Place baking sheet into the oven on the center rack. Bake for 11-12 minutes. Cookies will still be quite soft, let rest on the baking sheet for 3 minutes, then transfer to a cooling rack.
Store cookies in an airtight container. They will keep up to a week but be the freshest the first 3 days.
