First, let’s tackle ratios. The substitution should work as a 1:1 ratio, with 1 cup of creme fraiche equal to 1 cup of mascarpone. And you’ll add in the crème fraîche at the same time you would the mascarpone, usually folding it into the eggy custard. Like mascarpone, it would be best to bring crème fraîche to room temperature to mix smoothly and evenly into the filling.
Though the two are comparable in level of richness and texture, there will be a slight change in flavor as creme fraiche has a significantly more acidic finish. Mascarpone, in contrast, is beloved for its mildly sweeter character. Still, look at this change in taste as an opportunity to experience a nuanced twist on the classic tiramisu flavor. This is easier and faster than making your own mascarpone, so it’s worth a try. After all, it’s better to have some delicious tiramisu than none at all.