Preheat oven to 425˚F.
Arrange potatoes on a second baking sheet and season with salt, pepper, and granulated garlic. Cover with foil.
Poke the sausages with tines of a fork.
Roast cabbage and onions 20 minutes, then remove foil and add sausages. Roast until they are cooked through, 20-30 minutes more.
Roast the potatoes 20 minutes, then remove foil and roast until crispy and golden, 20-30 minutes more.
Melt butter in skillet and when foam subsides, add sage leaves. Crisp leaves and brown the butter, then remove the sage leaves to towel. In another skillet, add maple syrup and mustard. Mix together and let it warm through. Arrange the potatoes, cabbage, sausage, onions and garlic on a platter, drizzle the brown butter and maple mustard over everything, add sage leaves and serve.