http://www.epicurious.com/recipes/food/views/tiramisu-351138

Stir together water, espresso powder, 1 tablespoon sugar, and Tia Maria in a shallow bowl until sugar has dissolved, then cool.
Beat egg yolks, Marsala, and remaining 1/2 cup sugar in a metal bowl set over a saucepan of barely simmering water using a whisk or handheld electric mixer until tripled in volume, 5 to 8 minutes. Remove bowl from heat. Beat in mascarpone until just combined.
Beat cream in a large bowl until it holds stiff peaks.
Fold mascarpone mixture into whipped cream gently but thoroughly.
Dipping both sides of each ladyfinger into coffee mixture, line bottom of a 13- by 9- by 3-inch baking pan with 18 ladyfingers in 3 rows, trimming edges to fit if necessary. Spread half of mascarpone filling on top. Dip remaining 18 ladyfingers in coffee and arrange over filling in pan.
Spread remaining mascarpone filling on top and dust with cocoa. Chill, covered, at least 6 hours.
Let tiramisu stand at room temperature 30 minutes before serving, then dust with more cocoa.

Cooks' Notes
•You can substitute 2 cups freshly brewed espresso for the water and instant-espresso powder.
•Tiramisu can be chilled up to 2 days.