I love to take a regular recipe and add to it to create something new. That's what happened here. I modified my usual brownie recipe and this is the result. I tried it out at my last church potluck and everyone raved about them! There wasn't a single one left! I hope you enjoy them as much as we do.
Adjust oven rack to the middle position and heat the oven to 350 degrees. Line a 9 X 13 pan with foil, then coat lightly with vegetable oil spray.
Using and glass measuring cup or glass bowl, melt the butter and grated unsweetened chocolate together in the microwave for 2 minutes on 1/2 power. Remove and continue to stir until fully blended together. Set aside to cool.
Whisk the sugar, eggs, vanilla and instant coffee/espresso together in a large bowl until combined.
In another medium bowl, combine the flour, baking powder and salt.
Add the chocolate mixture to the other wet ingredients. Whisk until smooth. Add the dry ingredients to the wet and whisk until no streaks remain.
Scrape the batter into the prepared pan and smooth the top. Sprinkle the nuts on top of the unbaked batter. Bake until a toothpick inserted into the center comes out with just a few crumbs attached, 40 to 45 minutes.
After removing from the oven, pour the marshmallows over the hot brownies in an even layer. Place back in the oven for 1 minute under the broiler. DO NOT raise the rack of the oven. Remove brownies from oven. Marshmallows should still be white or just barely browned on top. Turn off oven. Sprinkle the chocolate chips on top of the marshmallows evenly. Place back in the warm oven for 1 1/2 to 2 minutes. Remove from the oven and, using a spatula, smooth the melted chocolate chips over the marshmallows.
Let brownies cool completely on a wire rack to room temperature, about 2 hours, before removing the brownies from the pan using the foil sling and cutting into squares.