Multi tasking while baking a büche can be stressful. It's a complicated bake. So when I attempted a chocolate sponge and got a brick instead, well, I decided to try again. This time, I wanted to try using soy lecithin powder.  Google led me to this fabulous formula from Roberta Pezzella, a vegan pastry baker who works for Gabrielle Bonci. Despite previous doubts about modernist food (nevermind the vegan approach) but heck, this made an awesomely healthy butter cream.  Moist and airy, and with fabulous flavor, nevermind sugarless, too. At least sorta!