The base is a so-called German buttercream. This is not widely acclaimed. When I look around at inspiring cake makers, they all use "Swiss meringue buttercream." This consists of a lot of egg whites with butter and sugar. In a vegan version, this is not possible. Of course, there is Aquafaba, which can be whipped in a comparable way, but in my experience, it's simply not as stable in the long run and tends to separate from the fat if you dare to look at the cream crookedly after cooling it. And ultimately, it is just whipped brine from canned chickpeas. Nothing against Aquafaba! I think the person who discovered that the liquid from cooked chickpeas behaves similarly to egg whites deserves a Nobel Prize! The protein consists of water and protein. When whipped, the proteins form a protective shell around increasingly smaller air bubbles and stabilize them. Together with sugar, airy meringue is created. The same goes for Aquafaba, as the chickpeas are the source of the protein. However, its intensity is naturally lower. You can boil it down. You can also process the sugar into syrup and add cream of tartar to stabilize the plant-based meringue (that would be "Italian meringue buttercream"), but for me, that's simply too much effort. And time is money in a small business.
So, I tried a lot, experimented, tasted, and then came back to German buttercream. It consists of 70 percent vanilla pudding, which wonderfully balances the high fat content, gives a subtle flavor, and a creamy texture. It doesn't require a trillion eggs to create a fluffy cream that is stable and tasty, just patience.
First, the pudding must be cooked and cooled completely to room temperature. While it rests, the soft but not flowing fat must be whipped. This takes about half an hour and a lot of scraping from the edge and bottom until even the smallest pieces are dissolved and beaten. The best indicator is an off-white color - best described in German as eggshell white - but also about a tripled volume in the bowl. A lot of air is incorporated. Now, food coloring or thickened fruit puree should be worked in if desired, namely before adding the pudding. The pudding must be stirred smooth and passed through a sieve beforehand to prevent small lumps that would be visible on the cake.
The finishing touch now comes - at the lowest speed, pudding is gradually added to the whipped fat, incorporated, and the airy cream is stirred a bit more finely porous, so that it then appears smooth and flawless on the cake.