Step 1: Make the Mascarpone Cream
In a large mixing bowl, use a hand mixer (or a stand mixer) on medium speed to beat the cold heavy cream until it begins to thicken. Gradually add the sugar and vanilla, continuing to beat until stiff peaks form. Be careful not to over-whip, or it will turn grainy. Gently fold in the room-temperature mascarpone cheese using a spatula until fully incorporated. Set aside.
Step 2: Prepare the Coffee Mixture
Pour the cold espresso or strong coffee into a shallow bowl. If using, stir in the coffee-flavored liqueur. This mixture should be deep enough to quickly dip the ladyfingers but not so much that they become overly saturated.
Step 3: Assemble the Tiramisu
Working one at a time, dip each ladyfinger into the coffee mixture for about 1-2 seconds per side. They should absorb some coffee but still hold their shape. Arrange a single layer of soaked ladyfingers in the bottom of an 8×8-inch baking dish. Spread half of the mascarpone cream mixture evenly over the ladyfingers, smoothing it out with a spatula. Repeat with another layer of dipped ladyfingers, followed by the remaining mascarpone cream.
Step 4: Finish and Chill
Using a fine mesh strainer, generously dust the top with cocoa powder. Cover the dish and refrigerate for at least 3-4 hours, or preferably overnight, to allow the flavors to meld and the texture to set.
Step 5: Serve and Enjoy
Once chilled, slice into squares and serve directly from the dish. For an extra touch, garnish with chocolate shavings or fresh berries.