Serves 6 Prep time 40 mins, cook 1 hr 55 mins Preheat oven to 200C. Remove thigh bones from chicken with a sharp knife (discard bones). Rinse chicken, pat dry with absorbent paper and set aside.
Heat a large non-stick frying pan over high heat. Add 20gm butter, cook chicken in batches skin-side down, turning once, until golden (5-7 minutes). Transfer to casserole, set aside. Add vegetables, garlic, 100gm bacon and 50gm Swiss browns to pan and stir frequently until golden (5-7 minutes), transfer to casserole. Deglaze pan with wine, add to casserole with stock, porcini and herbs. Roast, covered, until breasts are just cooked through (15-20 minutes). Remove breasts from casserole, set aside and keep warm. Return casserole to oven, cook until legs are cooked through (10-12 minutes). Remove legs from casserole and keep warm. Strain liquid into a saucepan (discard solids) and cook over medium-high heat until reduced to sauce consistency (20-30 minutes), return chicken to sauce to warm through.
Meanwhile, heat 30ml oil in a large frying pan over medium heat, add onion and stir frequently until golden (5-7 minutes). Cover with foil, stir occasionally over low heat until tender (15-20 minutes). Set aside, keep warm.
For porcini sptzele, combine flour and porcini powder in a large bowl, form a well in the centre. Combine cream, egg and 75ml water and add to well, then slowly whisk in flour from sides of well until a thick batter forms. Meanwhile, bring a large saucepan of salted water to the boil. Push small batches of batter through a colander with a spatula into boiling water, cook until sptzele rise to the surface (1-2 minutes). Transfer to a baking-paper-lined tray, lightly drizzle with oil to prevent sticking. Repeat with remaining batter.
Heat remaining oil in a large saucepan over medium heat, add remaining bacon and stir occasionally until golden (5-7 minutes), add remaining mushrooms and cook until starting to colour (2-3 minutes), add sptzele and stir until golden and slightly puffed (3-4 minutes), set aside and keep warm.
Blanch Brussels sprouts until bright green (2-3 minutes), refresh, drain, set aside. Heat remaining butter in a frying pan over medium-high heat, add Brussels sprouts, stir occasionally until golden (4-6 minutes), add to sptzele mixture with reserved pearl onions, season to taste, keep warm.
Divide sptzele and chicken between plates, spoon over sauce, top with sage and serve.
