Vertical assembling is essentially rolling a sponge cake with a filling inside. The biscuit shouldn’t break or crumble in the process. You have to choose a ductile biscuit. It has to be soft and elastic. Such biscuits are 90% composed of three main ingredients: eggs, flour, sugar. And only the remaining 10% are the flavoring additives and consistency "improvers" like nut pastes, nut flour, starch, baking powder or vegetable oils. You better use the classic vanilla sponge biscuit, almond biscuit, Japanese custard biscuit, or pistachio sponge biscuit. Butter-based biscuits like Victoria or brittle Red Velvet and Carrot biscuit are absolutely not suitable!
Let's say “no” to all the unstable crème types, as they will flow out in the process; they will not “grab” the layers of the biscuit together. Also, the crème with a high content of butter will not work, as the fat crème can peel off the biscuit when cooled. What crème should you choose? The best options are thick cheese-based crèmes of a medium fat content (cream cheese / mascarpone + powdered sugar + cream 33%). Such crèmes don’s flow, adhere the biscuits perfectly, and have nice taste. It’s also easy to turn such a crème into chocolate, caramel or nutty version.
Confit, confiture, compote… You better choose the thicker options (like cornstarch-based confit). It’s also great to use the pectin-based fillings.
The sponge biscuit and the filling should be cold; the crème should be just made (fresh), that’s obvious. You don’t have to soak the biscuits too much: if the sponge biscuit is thin, then it will be juicy even without soaking. Be sure to wrap the assembled roll tightly in a film, and let it rest in the fridge in the STANDING position for at least 8 hours. Don’t put the roll on its side, as it can deform under its own weight!
The coating crème and decoration don’t differ from the ones in the ordinary cakes recipe.