Make the coffee syrup by stirring the sugar into the hot coffee until dissolved. Set aside to cool slightly.
Beat the cold mascarpone, heavy cream, powdered sugar and vanilla on medium speed for 1-2 minutes, just until thick, smooth and spreadable. Don't overbeat, or the cream can turn grainy. Refrigerate until needed.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda and salt.
Stir the espresso powder into the hot water until dissolved, then whisk in the buttermilk, melted butter and vanilla. Pour into the dry ingredients, fold until just combined and let the batter rest for 10 minutes.
Heat a nonstick skillet or griddle over medium-low heat and grease it lightly with butter. Pour 1/4 cup of batter per pancake and cook for 2-3 minutes, until bubbles form, then flip and cook for 1-2 minutes more.
To assemble, brush the top of each warm pancake with coffee syrup. Stack them with a generous layer of mascarpone cream between each pancake.
Top the stack with a final dollop of mascarpone cream, dust with cocoa powder through a fine mesh sieve and finish with grated dark chocolate. Serve right away.