Combine 2 tablespoons demerara sugar with 1 cup brewed espresso and set aside

Slightly reduce ¼ cup Marsala wine in a saucepan until it reaches about 2 tablespoons

Whisk 4 large egg yolks with ½ cup demerara sugar in a bowl, making sure to stir constantly to avoid burning the eggs

Stream the warm reduced Marsala into the egg yolk mixture while whisking

Add 1 teaspoon vanilla extract to the mixture

Set up a double boiler with water coming just under a simmer

Place the bowl with the egg mixture on top of the double boiler and beat with a hand mixer on medium-low, increasing to high speed, for about 10 minutes until the mixture becomes light, mousy, and thick

Continue beating the zabaglione off the heat for several more minutes to cool it down

In a separate bowl, whip 1 cup heavy cream and 8 ounces mascarpone cheese together on medium-low speed, increasing speed as it thickens, until it reaches medium to stiff peaks

Fold the cooled zabaglione into the whipped cream and mascarpone mixture using a large spatula with a scraping and folding motion

Quickly dip each ladyfinger into the espresso soak for about 1 second on each side

Layer dipped ladyfingers in the bottom of an 8x8-inch shallow baking dish

Spread half of the filling mixture evenly over the first layer of ladyfingers using a small offset spatula

Repeat with another layer of dipped ladyfingers

Top with the remaining filling mixture spread in an even layer

Cover with plastic wrap to prevent a skin from forming

Refrigerate for at least 12 hours to allow the ladyfingers to hydrate and the filling to set

Before serving, grate chocolate or sprinkle cocoa powder over the entire surface

Cut into squares and serve