Has anyone done this successfully? I've read that you can blend ricotta with some heavy cream but am unsure of proportions, or whether it actually works.
I'm going to say no. If you can only get ricotta, make cannolis!
So - I have never made tiramisù with ricotta before - but by browsing some of the recipes that popped up online, it seems many of them include a sizeable portion of whipped cream alongside the ricotta in the mixture. I'm assuming that's because the ricotta is somewhat denser and has a grainier texture than mascarpone, and this is a way of getting a creamier mouthfeel.
It might be necessary to drain off excess water from the ricotta using cheesecloth or a clean tea towel. You really don't want too much liquid settling in your tiramisù as the savoiardi will already have been soaked in espresso.
I wouldnt- I make a lot of tiramisu and I think the ricotta would have too much of a grainy texture. But I have subsituted half cream cheese and half whipped cream. It has a slightly more cheesy (cheesecake) taste but the texture is almost exactly the same. By the way, if you cant find marscapone but can get your hands on some unpasteurized cream, you can make your own and its stupidly easy: