700 g (1 lb 9 ounces) peeled, sliced onions
120 g (4-1/2 ounces) butter
half teaspoon salt
half teaspoon pepper
160 g (5-1/2 ounces) caster sugar
7 tablespoons sherry vinegar
2 tablespoons red-wine vinegar
250 ml (9 fl ounces) red wine
Melt the butter in a heavy-based pan, and tumble in the sliced onions. Gently cook the onions until they have softened, then add the sugar and cook until the whole has turned a rich red brown color. Pour in the red-wine vinegar and simmer until it has evaporated. Then do the same with the sherry vinegar. Add the red wine and the seasonings, and simmer for an hour or two, until the jam has thickened and the onions have little bite left. Once the mixture has cooled slightly, pour into clean and sterilized jars, and seal.