Making tiramisu is an exercise in patience and an artistic challenge for even the most seasoned chefs. The ultimate consistency of tiramisu is a creamy but firm custard on the inside, meaning you will likely perfect your technique over multiple attempts. Tiramisu typically firms up when refrigerated, and can be frozen for future use.
Low Boil and Slow Chill
Freezing is not a technique to compensate for runny or overly soft tiramisu. Once frozen, it is not palatable until it is thawed out again. If it is not firm enough when you freeze it, you will find that it is still too soft when you thaw it out again. Focus instead on creating the proper consistency before you freeze a batch of tiramisu. The custard, which is called zabaglione in Italian, thickens when you cook the mixture over low heat in a double boiler. Follow directions for your particular recipe, but the slow boiling process will generally take about 8 minutes. Refrigerate for at least 4 hours or overnight to ensure that it is thoroughly chilled and firm.