Preheat oven to 350°F and line a cupcake tin with cupcake wrappers. Set aside.
In a medium-sized bowl, combine the flour, salt, and baking powder. Whisk to combine. Set aside.
In a large bowl, whisk together sour cream and sugars until a paste forms. Add the vegetable oil and whisk to combine. Add the eggs, vanilla, and coffee and whisk until combined.
Add the dry ingredients to the wet ingredients, whisking until just combined and no streaks of flour remain. DO NOT OVERMIX.
Evenly divide the batter amongst the 12 cupcake spots in the pan, (filling each about 2/3 of the way up) and bake for 20 minutes or until golden brown and risen. As soon as the cupcakes are removed, poke 6-10 evenly distributed holes into the top of the cupcake with a toothpick or wooden skewer.
For the Syrup:
Add the sugar, hot water, espresso powder and liqeur to a small bowl and whisk until the sugar dissolves. Use a pastry brush to brush the syrup over the cupcakes as soon as they come out of the oven. It is better to do this while the syrup and cupcakes are hot. Add more syrup than you think is necessary to get the full effect of the flavor.
For the Frosting:
Add the mascarpone and heavy whipping cream into a medium sized bowl. Whip on high speed with a hand mixer until thick and stiff peaks form. Add the liqueur, espresso powder, and powdered sugar. Mix until combined.
Use a piping bag to create nice swirls of frosting on the cupcakes. Dust the top of the frosting with the cocoa powder.