Remove the trivet and heat the oil. Brown the chops on both sides, then the onion. Drain off any excess fat. Dilute the tomato puree in 4 ounces water. Pour into the pan plus 4 ounces dry white wine. Add sugar, herbs, salt & pepper. Close lid and bring to full pressure. Cook for 10 minutes. Release pressure quickly. Serve the chops on a hot plate. Mix 1 tablespoon corn flour with a little water, stir into sauce and bring to the boil, stirring continuously. Allow to cool a little; stir in the cream. Pour over the chops.