Mix together all the ingredients in a bowl except the butter and paprika. Season the mixture with the paprika and some salt and pepper to taste.
2 tablespoon homemade ketchup, 1 teaspoon homemade or Dijon mustard, ½ teaspoon chopped capers, 1 small onion, 1 teaspoon finely chopped chives, 1 teaspoon finely chopped tarragon, 2 anchovy fillets, 1 teaspoon Worcestershire sauce, Sea salt and freshly ground black pepper, A pinch of paprika