Mix together your plant-based milk and 4 tablespoons of plant-based yogurt in a sterile jar.
Leave to ferment at room temperature for 3-4 days. The longer you leave it to ferment the more acidic it will become.The milk should have thickened up and be yogurt-like.
Once you are happy with the texture and degree of acidity, add any sweeteners or flavour agents. Simply mix through and taste and adjust to your taste.
Store in the fridge for up to a week. The yogurt will continue to ferment just at a slower rate. Taste and adjust any seasoning till you reach a flavour you like.