Place the mixing bowl and whisk attachment for the frosting in the fridge while you make the brownies.
Preheat the oven to 350°F/175°C. Grease an 8×8 pan and line it with parchment paper, making sure it overhangs the sides.
In a small bowl, whisk together the flour and salt.
½ cup all-purpose flour, 1 teaspoon kosher salt
In a large jug or bowl, whisk together eggs, egg yolk, sugars, oil, espresso powder and vanilla extract until smooth.
2 eggs, 1 egg yolk, ¾ teaspoon vanilla extract, ½ cup light brown sugar, ½ cup granulated sugar, ¼ cup vegetable oil, ¼ teaspoon espresso powder
Melt the butter in a large microwave safe bowl. Add the chopped chocolate and let it sit for a few minutes, then whisk until smooth. If the chocolate hasn't melted you can microwave for 10 second increments until melted.
4 ounces dark chocolate, 5 ½ ounces unsalted butter
Add the cocoa powder to the chocolate mixture nd whisk until smooth
¼ cup cocoa powder
Pour the sugar mixture into the chocolate mixture and whisk until smooth.
Add the flour mixture and fold, making sure there are no air pockets. I recommend using a rubber spatula for thise.
Pour the brownie batter into the prepared tin. Bake for 25-30 minutes, a toothpick inserted will have a few crumbs. Let cool completely in the pan.
Make the frosting. Beat the cream cheese in the (cold!) bowl of a stand mixer or in a large bowl with a hand mixer until smooth.
3 oz cream cheese
Add the confectioners' sugar, pinch of salt and vanilla extract and beat for 2 minutes on medium-high speed until smooth.
5 tablespoons confectioners' sugar, ½ teaspoon vanilla extract, pinch salt
Slowly pour in the cold heavy cream while you mix on low speed. Turn the speed up to high and whip until you have stiff peaks (about 1-2 minutes). Don't over mix this as it will become liquidy! To check if it's stiff enough, take the whisk attachment off of the mixer and dip into the frosting - the peaks on the whisk should stay firm and not lose shape.
½ cup heavy cream
Place the bowl of frosting in the fridge for about 30 minutes to firm up.
Take the brownies out of the baking pan and spread the frosting over the brownies. Slice and serve!
Notes
Temperature for Ingredients: I usually recommend having all of your ingredients be at room temperature before starting, but you want the cream cheese and heavy cream for the frosting to be cold - keep them in the fridge until you're ready to start making the frosting! Butter: I use European style butter in this recipe but you can use American butter if that is all you have.Heavy Cream: if you're based in the UK you can use double cream.Cream Cheese: if your cream cheese comes in tubs and not packets, you'll need to gently pat it down before using for the frosting. Cream cheese in tubs has a higher moisture content. Salt: If you don’t have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt. Please note, this is diamond crystal salt and not Morton salt, which is much too salty for this. Storage: Keep the frosted brownies in an airtight container in an airtight container for up to 4 days.