In a large bowl, whisk the melted butter and granulated sugar together until completely blended.
Whisk in the eggs, one at a time, and the vanilla extract until all ingredients are combined. The mixture should be thick and bright yellow. Set aside.
In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt.
Sift dry ingredients into the wet ingredients in small amounts, gently stirring with a wooden spoon or spatula between additions until all ingredients are completely combined.
Fold the ½ cup of BROWNIE mini marshmallows and the ½ cup of BROWNIE chopped nuts into the brownie batter using a few swift strokes.
Pour the brownie batter into the prepared baking pan and bake at 350F for 30 minutes, until brownies are almost done.
Remove the brownies from the oven and sprinkle the ½ cup of TOPPING chopped nuts, ½ cup of TOPPING mini marshmallows, and the chocolate chips over the top of the brownies.
Return brownies to oven and bake for 3-5 more minutes, until the marshmallow topping is poofed and lightly brown. Watch it carefully – don’t let it burn!
Remove Rocky Road Brownies from the oven and let cool slightly before serving.