Preheat the oven to 375 degrees. Spray a 9x13-inch baking pan with nonstick cooking spray.
In a small saucepan, melt the bittersweet chocolate and butter, stirring constantly until fully combined. Remove from the burner and let cool.
In a large mixing bowl, whisk together the granulated sugar, eggs and vanilla extract until smooth. Add the flour and salt and stir well until combined. Drizzle the chocolate mixture in, a little at a time, stirring constantly until combined. Stir in 1 cup chocolate chips, ½ cup mini marshmallows and ½ cup chopped pecans.
Pour the batter into the prepared pan, taking care to evenly distribute it. Sprinkle with the remaining chocolate chips, marshmallows and pecans.
Bake for 18-20 minutes, until a toothpick inserted into the center of the brownies comes out cleanly.
Let cool slightly before cutting into squares.
Recipe by Maine Course at http://mainecourse.bdnblogs.com/2017/02/14/recipes/camaraderie-and-rocky-road-brownies/