Take butter in a pan and add chopped onion and thyme and cook on a low flame. Add salt, cracked black pepper, Worcestershire sauce, red vinegar, mustard paste, vegetable stock, mushrooms and mix well. Take refined flour In a baking tray and keep it in an oven to make it brown in colour. Transfer the roasted refined flour to a bowl, add soup, mix it and blend it in a mixer. Add this paste to the soup and mix well. To the soup, add cracked white pepper, turn off the gas and pour the soup into a serving bowl. Cut the bread slices with a ring cutter and keep it in the oven till it turns slightly brown in colour. Add grated cheese on the bread and place the bread on the soup. Keep the soup in the oven. Later, remove the soup, garnish with chopped chives and serve.