What can i use instead of sherry? Can i use 1 3/4 teaspoon coffee?

Coffee or a coffee liqueur would work, but if you have Marsala, I'd use that - it's often an ingredient in Tiramisu and like Sherry is a fortified wine, in the same flavor family.

Coffee would work or increase the espresso powder by 1/2 tsp and use 1 3/4 tsp water or vanilla or better yet..use brandy.