To make the filling, Into a double boiler, combine egg yolks and sugar. Stirring constantly, cook for 10 minutes. Remove from heat and pour into a large bowl. Using a mixer, whip for two minutes until mixture is thick and has cooled slightly, then mix in mascarpone

In another bowl, whip cream until stiff peaks form. Fold into egg yolk mixture and set aside.

Stir together the espresso and liquor pour into a shallow dish, and set aside.

To make Lady Fingers, in a small bowl combine the cornstarch, potato starch, baking powder, and xanathan.

In a large bowl beat together egg yolks, sugar, vanilla, and water until smooth. Then beat in starch mixture until smooth.

In another bowl, whip egg whites with salt and cream of tartar until soft peaks form. Pour whipped egg whites into other mixture and gently fold until smooth. Batter will be loose.

You can bake them two ways: 1) Spoon into a piping (or ziploc) bag and pipe into 3" long shapes onto a parchment lined baking sheet. They will spread a bit, so space them out. 2) pour entire mixture onto a parchment lined baking sheet, and spread out evenly (this way you can cut the lady fingers out after they are cooked to exactly fit the pan you are using to prepare the tiramisu).

Bake at 375°F for about 10 minutes, or until edges just start to turn golden. Remove from oven and allow to cool 10 minutes before transferring to a rack. Cool completely before using in the tiramisu.

To assemble tiramisu, dip the lady fingers quickly into the coffee mixture on each side - do not let them sit and soak or they will fall apart. Arrange the lady fingers into the bottom of a 9" square baking dish. If your lady fingers are thin, add another layer of soaked lady fingers.

Spoon half of the cream filling over, and gently spread out.

Repeat process with another layer of lady fingers (double in necessary) and cream.

Refrigerate at least 4 hours or overnight.

Before serving, dust with cocoa powder and or shaved bittersweet chocolate.