Prepare 9x13 pan lining with aluminum foil and lightly grease foil.
Cut butter into 1 inch slices and melt over low heat in a small, heavy saucepan. Add the chocolate chips and whisk until melted. Turn off heat and leave set.
Using a large whisk, lightly beat eggs in a large mixing bowl.
In another bowl, add sugar and salt and mix then add to egg mixture until just incorporated.
Whisk in the melted chocolate/butter mixture and the vanilla together briefly.
In another bowl, whisk together the flour and cocoa powder together well.
Sift flour mixture over batter and mix together.
Pour batter into prepared pan, spreading evenly and bake for 24 minutes.
Remove pan from oven and add sprinkle marshmallows over brownies and transfer back to bake for an additional 6 minutes.
Sprinkle chocolate chips and M&M Easter Egss on top and place back in over for 1 minute.
Transfer pan to cooling rack.
To Make Chocolate Drizzle
Melt butter and syrup/honey together in saucepan you used for melting chocolate earlier over low heat. Add chocolate chips and stir together until melted. Stir in very hot water to thin out. Use spatula or spoon to drizzle chocolate across the marshmallow brownies.
Let brownies sit for 15 minutes and then refrigerate until ready to serve.
Remove brownies from pan by lifting out foil and then cut brownies and devour!
12 large or 24 small Divide recipe in half for 8x8 or 9x9 pan.