cup whole milk
cup sugar, divided
teaspoon pure vanilla extract
8-ounce containers mascarpone cheese
cup coffee, cooled to room temperature
cup brandy or rum (optional)
Cocoa powder, as needed for finishing
Place four 6-ounce glasses on a small baking sheet. In a small pot, heat the milk and ⅓ cup sugar over medium heat. In a medium, heat-safe bowl, whisk the egg yolks with the remaining ⅓ cup sugar and the vanilla extract. 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. 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. 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. When the custard is cool, whisk in the mascarpone until fully combined. 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. Scoop ¼ cup of custard filling on top of the cookies (the glass should now be about ⅓ way full) in each glass. 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. Refrigerate the tiramisu for 30 to 45 minutes. Sprinkle cocoa powder over the surface of the tiramisu, and serve chilled.