Rose Custard and Rhubarb Tarte

I came across a beautiful photo of this dish on Pinterest, read that it combined rose and rhubarb, and I knew immediately that I had to give it a try. It's from a blog written in Polish, of which I don't understand a word, but luckily, there's Google Translate.

I didn't follow the recipe for the shortcrust pastry as I didn't have sour cream (and to be honest, I'm not quite sure I would have dared to do that - sour cream in a shortcrust pastry?). Instead, I used the Sweet Pastry from Ottolenghi, which worked perfectly.

I made the rhubarb and the rose 'custard' according to the recipe. I put custard in parenthesis, as it's not really a custard, rather an egg-mascarpone cream. Unfortunately, the very last sentence is pretty bungled by Google Translate so I can't say for sure if the cream should be heated, but I'm quite sure that the recipe says it should only be cooled, then poured into the pastry. This is very unfortunate, as at least in my case, the cream was completely liquid, and there was no chance at all that the rhubarb would stay in top. Just in case the cream was meant to be cooked I tried that as well, but to no avail. I'm wondering what might have gone wrong - is her 'one package of mascarpone' considerably more than mine (250g)? Did she actually use less than 2 egg yolks? Or maybe you need to use gelatin (the last sentence actually mentions gelatin, but I understood that to be used for any juices the rhubarb released)?

All that said, flavourwise, it's absolutely fantastic! Really brilliant! It's a bit of a shame of the custard/cream, but if you omit (one) egg yolk, and/or add gelatin, it just might work.