Roast your garlic by peeling, wrapping in foil and popping in the oven for approx 20 minutes at 200-220°C until browning.
Peel the potatoes and then boil with carrots, yellow capsicum (yellow pepper), onion and carrots for approx 25 minutes. You can tell when this is ready by piercing the potato with a fork - if nice and soft then the vegetables are done.
Drain the liquid then put the potatoes into your food processor first and blend until you get it nice thick and mushy. Then, add the garlic, carrots, yellow capsicum and onion and blend again until they, too, become completely blended into a constant mushy texture with no visible solid bits.
Now, add every other ingredient in the list above (with water being slowly added) until you get a nice smooth consistency. If you wish for a thicker sauce, add less water. Sometimes if I am making this cheese for other dishes, I use less water and then let it set in the fridge to create a lovely cheese for dipping and buddha bowls. For mac & cheese, I prefer to add all the water in slowly while blending as once we bake the dish, some of the extra fluid cooks off so it prevents it from drying out.
If you do let this set in the fridge, it will firm up a bit. So when using, if you want to thin it back down, heat it up on the pan and as required, add some extra water by the tbsp until you get to the desired consistency.