Start by brewing 3 cups of strong espresso in an espresso machine or mocha pot. Chill for 1-2 days.
Preheat oven to 475°F. To make savoiardi, start by whisking your 125 g egg yolks with 100 g sugar. Beat mixture in a stand mixer until quadrupled in size and pale yellow, stiff, and glossy.
In a separate bowl, whisk 190 g egg whites until airy, about 3-4 minutes. Add your 85 g sugar and whisk until stiff peaks form and mixture triples in size. It should be stiff, glossy, and opaque white.
Sift your flour and corn starch into the middle of a large sheet of parchment paper (or a bowl). Sift again, twice in total, to ensure the ladyfingers are airy.
Fold a spoonful of your stiff egg whites into your glossy egg yolk mixture until combined.
Add a couple spoonfuls of your flour mixture and repeat folding until no streaks are left. Repeat steps by adding egg whites and flour, folding gently until no streaks remain.
Fill a large pastry bag with half of your ladyfinger batter. Use a #13 star tip and pipe 4-5" long, thin strips of batter onto parchment or silicon-lined baking sheets. When you run out of batter, refill your bag with the other half.
Dust your ladyfingers with a light coating of powdered sugar. Then, place in oven to bake for 9-10 minutes. Keep the oven door slightly ajar with the help of a wooden spoon.
Remove ladyfingers from oven when they are lightly golden and slightly puffed. Cool completely.
To make mascarpone filling, start by separating 6 eggs. Place yolks into a glass or metal heat-proof bowl.
Heat a double boiler of water over medium-high heat until bubbling and steaming.
Add 75 g of the sugar to your egg yolks and whisk to combine. Immediately place over your double boiler and whisk constantly, until temperature reaches 85°C.
Remove egg yolk and sugar mixture from heat and add the other 75g of sugar and salt. Whisk to combine and let cool slightly.
Add mascarpone to the egg yolk mixture and whisk until cohesive and silky smooth.
To assemble tiramisu, spread a small layer of mascarpone cream in the bottom of a 10x10" square baking pan.
One at a time, dunk your ladyfingers in your chilled espresso (quickly) and place in a layer in your pan. Once you have a later with no gaps, place a couple spoonfuls of mascarpone cream on top and smooth into an even layer.
Repeat layering coffee-soaked ladyfingers and mascarpone cream until you have none left. Smooth the top of your tiramisu, ending with cream.
Dust a thin layer of cocoa powder and espresso powder mixture on top and cover pan with plastic wrap. Place in fridge to chill and develop flavors for 1-2 days. Dust with more cocoa and espresso powder before serving.