Heat the oil in a large pot over high heat. If the bacon is particularly fatty, the oil may be omitted. Add the chopped bacon and cook for approximately 2 minutes until it begins to render and brown.
Incorporate the onion and garlic into the pan, cooking for a further 3 minutes or until both the onion and bacon have developed a golden hue.
Introduce the beans, ketchup, tomato passata, molasses, vinegar, water, mustard powder, Worcestershire sauce, cayenne pepper, salt, and black pepper to the pot. Stir thoroughly to combine.
Bring the mixture to a gentle simmer, then cover with a lid. Continue to cook either on the stovetop at a reduced medium-low heat for 1 hour, stirring occasionally to prevent sticking, or transfer to an oven preheated to 160°C (325°F) and bake for 60 minutes.
For a slow cooker version, reduce the water to 1/4 cup, transfer the contents to the slow cooker, and cook on low for 6 hours.
Once cooked, the sauce should be thickened and glossy. If it appears too loose, simmer uncovered for a few extra minutes. Adjust the seasoning with additional salt and pepper to taste before serving.