Preheat oven to 350°F. Line a cookie sheet with parchment paper.
In a microwave or using a double boiler method, melt the butter and chocolate together until melted and combined together. Set aside while it cools and you prep the rest of your ingredients.
1 cup semi-sweet chocolate chips, 1/3 cup unsalted butter
Into a large bowl, whisk together the eggs, brown sugar, and white sugar. Whisk until paler in colour and bubbles form.
3/4 cups dark brown sugar, 1/4 cup white sugar, 2 eggs
Add in the chocolate butter mixture and whisk until well combined.
Add in flour, cocoa powder, and salt. Using a spatula, fold until a soft chocolate dough forms.
3/4 cups all-purpose flour, 1/4 cup unsweetened cocoa powder, 1/4 tsp salt
Add in chocolate chips and M&M's and mix in a few times.
1/4 cup semi-sweet chocolate chips, 1/4 cup regular sized M&Ms
Scoop 6 cookie dough balls at a time. Bake for 10-12 minutes or until the edges are crisp and the inside is still soft. As the cookie cools, it will continue to bake on the tray.
Remove from the oven and place the tray on your counter to cool. Sprinkle some flakey sea salt (optional but recommended!), and enjoy!