Peel onion and chop very finely. Bring to the boil in a pot with ketchup, sugar, vinegar, lemon juice, mustard, pepper, Tabasco and smoked salt. Simmer open for about 30 minutes, stirring several times. Season to taste once more. Pour hot into prepared clean glasses or bottles (500 ml each) and close them well. Store in a cool and dark place. Shelf life approx. 3 months.