If using sourdough place it in a large bowl, add a little milk and mix just enough to get a smooth and soft batter.
If using brewer's yeast, instead, dissolve it into a little milk. You will then add to the flour needed for the recipe (90g) 100g more, and 50ml of water.
Add all other ingredients into the bowl and start kneading with your hands, adding milk little by little and just enough to get a soft, elastic dough. If using brewer's yeast add 50ml water first then milk, if needed.
Divide the dough into six equal parts and shape the brioches as you prefer. Line them on a baking tray covered with parchment paper, brush with plant milk and let rise until doubled (about 3-4 hours).
Bake the vegan brioche buns in a preheated oven at 350°F for 18 minutes.
These vegan brioche buns keep well in a food bag up to 5 days. I suggest to freeze if you need to keep them longer.