In a pot add the olive oil and warm over low-medium heat. Add the flour and nutritional yeast and whisk for 1-2 minutes to cook off the raw flour taste.
Slowly pour in the plant milk (~ one cup at a time) while whisking continuously so the sauce stays smooth. Start with about 1 litre and add more if you prefer a thinner sauce.
Cook for around 5-8 mins, whisking often, until the sauce thickens to your liking.
Season with salt and pepper to taste (skip the salt if serving to babies under 12 months).
Store in the fridge for 3 days or freeze in portions for 2 months