In Texas and Mexico, Chilli con carne would typically be made using diced beef and a blend of 3 or 4 different types of chilli. In the British version we use minced beef, 1 type of chilli ('red'!) and beans, usually red kidney beans. So, not authentic, but very tasty.
Peel and chop the onion and sauté gently in a little oil on medium heat for about 5 minutes, until softened. Peel and mince the garlic and add it to the pan. After a minute or two, add the minced beef and break it up into small bits. Keep stirring until the beef is browned all over. If your tomatoes are already chopped, throw them in, otherwise you'll need to chop them. Add the stock, the passata, pepper and basil. Simmer for about 30 minutes.
At this point, you have your bolognese sauce. If you want to use some of it for Spag Bol, divide the sauce in half and stick it in the fridge. You can now go ahead and convert the bolonese sauce into chilli, or if you managed to plan ahead, put it in the fridge overnight - the flavour will improve dramatically.