Step 2

Place four 6-ounce glasses on a small baking sheet.

Step 3

In a small pot, heat the milk and ? cup sugar over medium heat. In a medium, heat-safe bowl, whisk the egg yolks with the remaining ? cup sugar and the vanilla extract.

Step 4

When the milk comes to a simmer, add it to the yolk mixture in a slow, steady stream. Whisk constantly as you add the milk, mixing until it's fully incorporated.

Step 5

Return the milk mixture to the pot and continue to cook, stirring constantly, over low heat until it thickens enough to coat the back of the spoon, 3 to 4 minutes.

Step 6

Pour the mixture into a heat-safe bowl and cover directly with plastic wrap. Refrigerate for 30 minutes, or until no longer warm to the touch.

Step 7

When the custard is cool, whisk in the mascarpone until fully combined.

Step 8

In a small bowl, mix the coffee and alcohol (if using) to combine. Working one at a time, dip a ladyfinger into the coffee mixture, submerging it for 10 to 15 seconds. Place 2 soaked cookies in the base of each prepared glass, you may have to break them into 2 or 3 pieces to fit--try to get an even layer in the base of the glass.

Step 9

Scoop ¼ cup of custard filling on top of the cookies (the glass should now be about ? way full) in each glass.

Step 10

Repeat the process, soaking more cookies and layering two soaked cookies into the glass, then top with custard. Repeat once more, for a total of 3 layers of cookies and 3 layers of custard, finishing with custard.

Step 11

Refrigerate the tiramisu for 30 to 45 minutes. Sprinkle cocoa powder over the surface of the tiramisu, and serve chilled.