If your tiramisu is already runny, you can try leaving it in the fridge to set for longer if you have time. Ideally leave the tiramisu to set overnight in the fridge, if you check it in the morning and its till not set you can leave it for an additional night and it should firm up.

Do you have to let tiramisu set?

Let the tiramisu set up for at least 6 hours, overnight is best. This tiramisu can be made a day or two ahead of time and should last in your fridge for up to a week.

Does tiramisu harden in fridge?

Most tiramisu recipes call for allowing the assembled dessert to chill in the refrigerator for several hours or overnight. This will give the ladyfingers time to absorb some of the moisture. Chilling also helps the fat in the cream solidify, giving the cream a firmer texture.