0 Espresso Soak: Combine the hot water and espresso powder in a shallow dish and whisk until the espresso is dissolved. Stir in the coffee liqueur. Set aside to cool.
1 Egg Mixture: In a medium heatproof bowl, whisk together the egg yolks and sugar until well combined. Fill a pot with about 1-2 inches of water and bring it to a simmer. Make sure the pot is large enough so the heatproof bowl can sit on top without touching the water (this creates a double boiler). Place the bowl with the egg yolk mixture over the simmering water and turn the heat to low.
2 Continuously whisk the mixture while it heats. Cook until the sugar is fully dissolved and the mixture turns pale in color, about 4-6 minutes. You can test this by rubbing a little of the egg mixture between your fingers - it should feel smooth, not gritty, and the temperature should reach 160°F on a digital thermometer. Once ready, remove the bowl from the heat and set aside.
3 Mascarpone Cream: In a large mixing bowl, or in the bowl of a stand mixer fitted with a whisk attachment, add the mascarpone cheese, heavy cream, and coffee liqueur. Start mixing on low speed, then gradually increase to medium-high until the mixture thickens. The mixture should reach stiff peaks, with no lumps remaining. Add the egg yolk mixture to the mascarpone mixture and gently fold it in, just until everything is fully combined.
4 Assembly: Working with half of the ladyfingers, quickly dunk one at a time into the espresso syrup until fully submerged. Arrange the soaked ladyfingers in a single layer in the bottom of a square 8”x8” pan, trimming them to fit as needed. Add half of the mascarpone filling on top of the ladyfingers and smooth it out into an even layer.
5 Repeat the same process with the remaining ladyfingers, dunking one at a time in the espresso syrup, creating another layer. Press down gently on the ladyfingers if needed to make the layer more even. Add the remaining mascarpone filling on top and spread it out to the edges of the pan, smoothing out the top with an offset spatula.
6 Cover the top lightly with plastic wrap and refrigerate the tiramisu for at least 4 hours, preferably overnight.
7 Decorating: Use a fine mesh sieve to dust the top of the tiramisu with an even layer of cocoa powder to fully cover the top. Slice, serve, and enjoy!
