What can I use in place of oil for cooking spag Bol ?

butter. I never use oil for cooking

Olive oil is best, and I would choose bacon fat as the next best choice. I wouldn't go with butter because it will impart a dairy flavor you probably don't want with tomato-based sauces, so if you don't have any rendered bacon fat, then choose goose fat.

My family's oldest spaghetti sauce recipe always used the fat rendered from a piece of salt pork.

Go with the goose fat.

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If you have it, render some streaky bacon or pancetta, if not, go with the butter.