Butter a 22 – 24 cm flan dish really well with soft butter and shake some of the fresh breadcrumbs into the dish so that the crumbs adhere to the bottom and sides. Reserve the remaining crumbs for the topping. Place dish in the freezer to set the crumbs while making the filling.
Adjust the oven rack to the middle position. Preheat the oven to 180°C.
Season the onions with Green Onion Seasoning. Sauté the onions in the oil/butter mixture until completely soft and beginning to brown slightly. Grate the unpeeled sweet potatoes on the coarse side of a grater and stir-fry with the onions until just cooked. Sprinkle the White Sauce Powder over and stir in. Remove from the heat and season with Potato Spice.
Beat the eggs with the sour cream and add the mustard. Add half the cheese. Stir the egg mixture into the sweet potato mixture.
Pour into the prepared dish. Toss together the remaining cheese, remaining breadcrumbs and Chilli & Garlic Seasoning and sprinkle over the Quiche.
Bake for ± 35 minutes until set and puffy. Serve with a fresh, well dressed green salad.