Preheat oven to 325 degrees and grease a 8 x 8 baking dish.
Make brownies according to package directions, stirring in the chocolate syrup after the batter is ready.
Pour half of your batter into your greased pan.
Layer one cup of marshmallows over the batter, then pour the remaining batter on top.
If any marshmallows are visible, gently tap them down into the batter with a toothpick so that none are visible.
We want the marshmallows to melt into the brownies as they bake!
Sprinkle the remaining cup of marshmallows on top and bake at 325 degrees for 45-50 minutes, depending on your oven.