Preheat oven to 350°F. Line an 8x8 inch baking pan with parchment paper, leaving a couple of inches hanging over the edges on each side.
In a large mixing bowl, whisk together the cocoa powder, flour, baking powder, and salt.
Add the melted butter, vegetable oil, eggs, both sugars, and vanilla extract. Stir until just combined. Do not overmix.
Pour the batter into the prepared pan and spread evenly.
Bake for 30 to 35 minutes, until the edges are crisp and the center is set.
Immediately spread the marshmallow creme over the top of the hot brownies. Use an offset spatula to create waves and peaks.
Return the pan to the oven and turn the broiler on. Broil for 2 to 3 minutes, watching very closely, until the tops of the marshmallow peaks are lightly toasted.
Remove from the oven immediately and set aside to cool completely to room temperature before slicing and serving.