Preheat the oven to 350F and line an 8x8 pan with two pieces of parchment paper which extend over the sides to give you a ‘"handles" (this helps with removing the slice easily once it is set).
In small bowl, whisk the flour, cocoa powder and salt to combine. Set aside.
Combine the chocolate, butter and espresso powder in a medium saucepan. Place over low heat on the stove. Stir until melted.
Remove the pan from the heat. Add in both the granulated and brown sugars and stir until combined. The mixture should now be room temperature. If not, let it cool just a bit before adding the eggs.
Add in the eggs, one at a time, stirring just to combine after each addition. Stir in the vanilla extract.
Stir in the flour mixture until just combined. Pour the brownie mixture into the pan and spread evenly with a spatula.
Bake the brownies for 20-25 minutes, or until a toothpick comes out with with moist crumbs.
Leave the brownies to cool to room temperature before adding the fudge layer.
In a medium saucepan, combine the white chocolate, sweetened condensed milk, and marshmallow fluff. Stir until melted and combined.
Remove the fudge from the heat. Stir in the peppermint and vanilla extracts.
Evenly spread the fudge mixture over the cooled brownies. Work quickly as the fudge will start setting up and will be hard to spread.
Refrigerate the fudge for about an hour or two, or until the fudge is cooled and set.
Combine the butter and chocolate in a microwave safe bowl. Melt the butter and chocolate in the microwave at 30 second increments until melted and smooth.
Spread the melted chocolate evenly over the fudge.
Top the chocolate layer with crushed peppermint pieces. Let the chocolate firm up before serving. Serve at room temperature.