Put a large skillet on a medium heat and add butter.
Add the onion and ground beef and cook, stirring occasionally, until cooked through, about 10 minutes.
Add sugar free ketchup, tomato paste, veal fond, basil and full fat cream.
Stir with a wooden spoon.
Bring to the boil and reduce to a gentle simmer. Cook for 15 minutes mins stirring occasionally, until you have a rich, thick sauce.