Preheat the oven to 350°F. Spray three 9-inch cake pans with nonstick spray with flour.
In a large bowl, combine the flour, 1 3/4 cups sugar, baking soda, baking powder and salt.
In a medium bowl, combine the water and espresso powder, stirring until the espresso dissolves. Add the oil and eggs, whisking until smooth. Add the espresso mixture to the flour mixture, beating at medium speed with a mixer until combined. Stir in the sour cream. Spoon the batter evenly into the prepared pans.
Bake until a wooden pick inserted in the center comes out clean, 18 to 22 minutes. Cool in the pans on wire racks for 10 minutes. Remove from the pans, and cool completely on wire racks. Brush each cake layer with 1 tablespoon coffee-flavored liqueur.
In a small saucepan, combine the chopped chocolate and 1 3/4 cups heavy cream. Cook over medium-low heat, stirring constantly, until chocolate is melted and smooth. Cool for 15 minutes.
Spread a thin layer of the chocolate frosting and then the Mascarpone Filling over one cake layer. Top with the ladyfingers, cut-sides up, cutting to fit if necessary. Top with a second cake layer, and repeat the procedure. Top with the remaining cake layer. Spread the remaining chocolate frosting on the top and sides of the cake. Store the cake, covered, in the refrigerator for up to 3 days.
In a medium bowl, beat the mascarpone and 1/4 cup sugar at medium speed with a mixer until creamy. Add 1/2 cup cream, beating until the mixture thickens. Cover and chill for up to 3 days. Yield: 2 1/2 cups.