posted 2 years ago
You might be better off looking at nuts and seeds for what you're talking about. Mayo is mostly oil. The egg is just an emulsifier, so you can also use cooked vegetables like eggplant or carrot, avocado, beans. The beans are always going to be secondary to the oil, though. Mayo is fat, not starch. So if you were to blend up a neutral tasting nut or seed until it's very smooth, that would work better for mayo.
For sour cream, take your favourite nut/seed, blend very smooth and add a starter of some sort. Could be juice from fermenting vegetables, could be probiotic powder, could be yoghurt starter, etc. Let it sit on the counter for a day or two. Keep tasting until it's got the level of acidity you want. There's your sour cream.
My favourite sour cream substitute is cultured coconut cream.