Get out all of your ingredients. Preheat your oven to 350 degrees.
Beat together butter, sugar, and eggs until fluffy, then beat in cocoa powder, flour, baking powder, and salt until fully incorporated.
Beat in milk until smooth, and then pour into a lined 9x9 pan, saving ½ - ⅔ cup for later.
Smooth surface as best you can.
Mix graham cracker crumbs and melted butter, and then sprinkle a generous layer on top of your brownie batter.
Top with a layer of chopped Twix bars and chocolate chips.
Add a layer of marshmallows.
On top of that, pipe out your remaining brownie batter in messy drizzles, then lightly spread it out just a bit where you have drizzled.
Add a few more marshmallows.
Bake at 350 degrees for 30 minutes or until a toothpick comes out clean and marshmallows are nicely browned. You can broil the top for a few minutes if desired. I never do.
Cut, serve and enjoy.