In a medium bowl, using an electric mixer set on medium speed, beat
together the mascarpone cheese, 1 c up of the confectioner's sugar and the Marsala until well blended.
Add the cream and beat until fluffy, about 1 minute. Set aside. In a small, heavy saucepan over high heat, combine the water, the remaining 1/2 cup confectioners' sugar and the espresso or coffee powder.
Bring to a boil, stirring occasionally.
Remove from the heat and let cool.
Using a long serrated knife, cut the cake crosswise into slices 1/4- 1/3 inch thick.
Select a 2 1/2-qt oval or rectangular glass or ceramic dish about 11 inches in diameter and 2 inches deep.
Arrange enough of the cake slices in a single layer over the bottom of the dish to cover completely, trimming to fit as needed.
Brush half of the cooled espresso syrup over the cake. Spread half of the cheese mixture evenly over the top.
Top with enough of the cake slices in a single layer to cover completely, trimming to fit as needed.
Brush the remaining cooled espresso syrup evenly over the top.
Then spread the remaining cheese mixture over the top.
Cover with pla stic wrap and refrigerate up to 2 days.
Using a fine-mesh sieve, sift cocoa evenly top just before serving.
Using a large spoon, scoop the tiramisu onto individual plates.