In a pot, add the peeled, large-diced sweet potatoes, a pinch of salt, and the bay leaf.
Boil until tender, then drain. Remove the bay leaf. Add the warm milk and butter, then mash until smooth.
Stir in the grated Gruyère until melted. Set aside.
Place both types of sausage, cut into slightly larger-than-bite-size pieces, in a baking tray. Roast in a preheated oven at 180°C / 356°F for 15 minutes.
Meanwhile, heat the ghee in a pan over medium heat. Add the onion, bell pepper, chili, and garlic. Cook for about 10 minutes, until softened.
Add the salt, black pepper, paprika, cumin, 7-spice mix, and flour. Cook for 2 minutes.
Add the frozen peas, then pour in the passata and water. Simmer on low for 15–20 minutes, until thickened and the peas are tender. Add a little water if needed.
Add the baked sausages along with any juices from the tray. Simmer for 5 minutes.
Transfer the mixture to a baking dish. Pipe or spoon the sweet potato purée over the top.
Sprinkle with Parmesan and place under the broiler/grill for 5–10 minutes, until lightly browned.
Serve with a simple salad or pickles.