I was wondering if you could help me with the quantities of minced beef, tinned tomatoes, onions, etc. I would need to make enough chilli con carne (with jacket potatoes rather than with rice so should need slightly smaller portions) for 40 people?
For a regular serving of chilli con carne you would allow between 110g and 150g (4 to 5 ounces) of minced beef (ground beef) per person and then to that add roughly one chopped onion and one can of tomatoes per 500g (1 pound) of meat. So you could probably reduce this to around 75g (3 ounces) meat per person if using the chilli as a topping for baked potatoes, if serving with items such as grated cheese and sour cream as well.
However it may be easier just to scale up an exisiting chilli recipe and one of the easiest to adapt for a large crowd would be Nigella's Conrbread-Topped Chilli Con Carne from Feast (p399). This recipe serves up to 20 and you can make the meaty sauce and serve it with baked potatoes, instead of with the cheesy cornbread topping.
As the quantities are so large we suspect that it would be easier to make this chilli in two batches. Chilli is a dish that is easy to make in advance and is often better if left overnight and then reheated. It also freezes very well. Cool and refrigerate the chilli as quickly as possible (you should refrigerate it within 2 hours of the cooking time). For large quantities it may be easier to transfer the cooked chilli to a wide, deep dish as this will help it to cool more quickly. Store in an airtight container in the fridge for up to 2 days or freeze for up to 3 months. If frozen then let the chilli thaw out in the fridge for 24 hours. Reheat the chilli over a medium heat, stirring regularly, and make sure it is piping hot before serving.