Whisk together the melted butter, brown sugar, granulated sugar, and vanilla extract.
Add in the eggs one at a time and whisk each one until fully incorporated and the batter starts to get lighter in color. To get crinkly brownie tops, be sure to whisk the sugar and eggs for at least 4-5 minutes (a hand mixer is very helpful for this).
Fold in the black cocoa powder, dutch cocoa powder, flour, espresso powder, and salt and mix until the batter is just combined. It will be thick.
Cut a parchment paper sling slightly smaller than the width of the cake pan and make sure it fits flatly in the bottom. Then lightly spray the bottom and sides of the pan with a vegetable oil based spray. Place you parchment paper sling in the bottom of the pan and smooth it out so that it sticks to the pan spray (you can use metal binder clips to secure it to the pan). After baking you’ll be able to just slide the brownies right out of the pan!
Smooth the brownie batter into the prepared pan.
Bake at 350°F for 30-40 minutes or until an inserted knife comes out mostly clean. You want the center to still just be slightly wet because the brownies will continue to cook as they cool.
Remove from the oven and let cool completely in the pan. Then remove using the parchment sling.
Marshmallow Spiderwebs
All you have to do is place the marshmallows in a microwave safe bowl (I prefer glass) and microwave for 10-20 seconds. Note the marshmallows will be very hot!
Stir the marshmallows until smooth and let cool for 1-2 minutes until you have a thick, stringy goop that is no longer hot to touch.
There are two options for spreading the marshmallows on the brownies: Use two forks to pull strings of the melted marshmallow and spread across the top of the brownies. Or while wearing disposable vinyl gloves, use your hands to spread the marshmallows across the top.
Notes
It's better to undercook the brownies slightly, than overcook them! Brownies will dry out quick, so it's best to err on the side of caution when baking brownies! Bake just until an inserted toothpick comes out mostly clean but still a tad gooey. If you aren't sure, just go ahead and take them out because they'll continue to firm up as they cool. Note: the larger the pan, the less time the brownies will take to cook.Be patient and let them cool. Warm brownies fresh out of the oven are delish, I know. But it's best to let them fully cool before digging in. The brownies will be less likely to crumble when you cut them and the center is more likely to be fully cooked while still being perfectly fudgy.Note: The square cake pans I use are between 2 ¼ and 2 ½ inches deep (so that you can get those super thick brownies). So if your pan happens to be shallower, you might end up with a little too much batter. So instead you can also bake these brownies in a 9x13 inch pan, just note the brownies will be much thinner than the photos.