In the bowl of a stand mixer fitted with the paddle attachment, beat the eggs, white sugar, brown sugar and vanilla on high for at least ten minutes. You need a meringue type consistency in order to create a crust on top of the brownies.

In a separate bowl, add the flour, cocoa powder, espresso powder and salt. Stir to combine.

In a microwave safe bowl, add the butter and chocolate. Microwave on high for 30 seconds, stir and repeat until chocolate has completely melted and is smooth.

While the stand mixer is on medium speed, slowly add the chocolate until mostly combined. Add the flour mixture and stir until just combined.

Grease and flour a 9x13 inch baking dish. Pour batter into dish and smooth out the top. Bake for 25 minutes or until the top is matte and a bit cracked. Don't over bake. The brownies will set as they cool. Allow the brownies to cool for 10-15 minutes before you top them with the marshmallows.

In the top of a double boiler, heat butter, butterscotch chips and peanut butter until melted. Remove from heat. Stir in marshmallows.

Pour mixture on top of brownies and carefully spread evenly. Allow the brownies and marshmallows to come to room temperature. Wrap the pan in plastic wrap and refrigerate until firm.

Cut into squares and serve!