6 large egg yolks
3/4 cup sugar
3/4 cup whole milk
Four 8-ounce containers mascarpone cheese, at room temperature
1 1/2 cups espresso or strong coffee, at room temperature
1/2 cup brandy or cognac
30 to 32 crisp Italian ladyfingers (savoiardi)
1/4 cup Dutch-process cocoa powder
Bittersweet chocolate, for shaving
Line an 8-inch square baking dish with plastic wrap, leaving a 3-inch overhang on all sides. Fill a large bowl with ice water.
Make the custard: Whisk the egg yolks and sugar in a heatproof bowl set over a pot of barely simmering water (do not let the bowl touch the water) until the sugar dissolves.
Slowly whisk in milk and cook, whisking constantly, until custard is light and fluffy, about 10 minutes (a thermometer inserted into the mixture should register 170 degrees F).
Remove bowl from saucepan and place in bowl of ice water; whisk until custard is cool, about 1 minute. Place mascarpone in a large bowl. Fold the custard into the mascarpone with a rubber spatula until almost combined, then whisk until smooth (do not overmix or the custard will be grainy).
Combine espresso and brandy in a shallow bowl. One at a time, dip ladyfingers in espresso mixture until soaked but not soggy; arrange 2 rows of about 5 cookies each in baking dish. Spread one-third of the mascarpone custard over the ladyfingers. Repeat with a second layer of espresso soaked ladyfingers, arranging them in the opposite direction. Top with another third of the custard. Repeat with remaining ladyfingers, alternating directions. Spread the remaining custard on top and dust with cocoa powder. Cover with plastic wrap; refrigerate at least 4 hours, or overnight.
Invert a baking dish over the top of the tiramisu, then invert the tiramisu with the dish. Remove baking dish and plastic wrap. Invert a serving plate on top of the tiramisu and flip again so it is on the cocoa side. Remove the remaining plastic wrap. Shave the chocolate curls off the top with a vegetable peeler.