Melt butter in a medium sized saucepan. Add onion and salt, cook over medium heat; 10min, stirring occasionally.
Add mustard and thyme; stir and cover. Continue to cook very slowly; 25min, onion will be super soft and simmering in its’ own liquid.
Add water and pepper. Simmer further 10min.
Serve topped with bread and cheese, see below.
Divide soup evenly across 4 small oven proof bowls.
Top each with 1 slice of bread and 1 slice of cheese.
Place soup under the grill, heated to high (or top shelf of an oven pre-heated to 180°C) until cheese is melted. Remove from grill using oven proof gloves.
Try using different low protein cheeses if preferred. Mozzarella and Pizza are also full of flavour.
This recipe has been specifically designed for a low protein diet. Refer to labels for allergen and other product information.