Prepare a large pan of boiling water.
If you wish, you can peel the potatoes (I prefer to leave the skin on). Cut the potatoes into halves or quarters, then into 0.5cm / ⅕ inch slices. Boil the potatoes for 10 minutes or until tender, then drain using a colander.
Meanwhile, heat ½ TBSP extra virgin olive oil in a large non-stick frying pan (skillet) on medium-low heat and cook the onions, stirring now and then.
Prepare the batter: place the milk, silken tofu, mustard, gram flour, nutritional yeast, cornflour, turmeric and black salt (if using) in a large mixing bowl and blend smooth using a hand blender (alternatively use a jug blender).
When the potatoes are tender, tip them into the frying pan with the onion. Add 1 TBSP extra virgin olive oil, 2 tsp garlic and ½ tsp salt. Continue cooking for a couple of minutes on medium heat, stirring regularly until the potatoes are fully coated in the oil and salt. (They should start to turn a light yellow colour). Taste test and add a touch more salt or oil, if needed.
Add the contents of the frying pan to the batter in the mixing bowl and stir through.