Assuming you mean the HP type of brown sauce:
Ingredients:
720ml malt vinegar
1 tbsp mustard powder
200ml water
2 tbsp black treacle
1 tbsp salt
2 tbsp Muscovado sugar
2 dessert spoons flour
3 tbsp tamarind pulp
3 tomatoes, chopped
60g dates, chopped
4 shallots, chopped
1/2 tsp freshly-grated ginger
4 whole cloves
6 allspice berries
4 black peppercorns
2 bay leaves
pinch or turmeric
pinch of cayenne pepper
1 star anise
1/2 tsp coriander seeds
a little oil for frying
Method:
Add the oil to a pan and use to fry the shallots until softened (about 6 minutes) then add the tomatoes and dates and cook for 4 minutes, or until the tomatoes begin to release their juice. Add the water, tamarind pulp and spices and bring the mixture to a boil. Reduce to a simmer, cover the pot and cook for 10 minutes. Take off the heat and set aside until cold.
Pass the mixture through a fine-meshed sieve, pressing with the back of a spoon to extract as much liquid as possible. Return this liquid to a pan and whisk-in all the remaining ingredients (except the vinegar, sugar and treacle). Bring to a boil over medium heat then stir-in the vinegar, treacle and sugar. Return to a boil and continue boiling, uncovered, for 5 minutes, stirring all the while.
Take off the heat and allow to cool a little before pouring into a bottle that's been sterilized and heated in an oven pre-heated to 120°C for 10 minutes. Securely seal the bottle then set aside to cook. Allow to mature in a cool cupboard for at least 3 weeks before using. Store in the refrigerator once opened.
