Preheat oven to 350 degrees. Line a 9x13-inch baking pan with a parchment paper sling or spray with cooking spray.

In a large bowl, cream together the butter and sugar until light. Add in the eggs and vanilla and beat until smooth. Add cocoa, flour, baking powder, salt, coconut, and 1 cup of the chopped pecans and stir to combine.

Pour the brownie batter into the prepared pan and bake in the preheated oven for 30-40 minutes or until a toothpick or sharp knife inserted in the center comes out clean.

While the brownies are baking, mix all of the frosting ingredients together and beat until smooth. Set aside.

Remove the brownies from the oven and Immediately top with the marshmallows. Wait 5 minutes, then sprinkle remaining chopped pecans on top.

To frost, scoop dollops of frosting over the soft marshmallows while the brownies are still hot and then gently spread or nudge the dollops of frosting around to touch each other. It won't be perfect because the soft marshmallows make it tricky to truly "frost" the brownies, but it will be okay if marshmallow pokes through in places. Frosting these brownies while they are still warm helps because the frosting will melt just a bit and make for extra gooey yumminess.

Cool, then cut into squares and serve.