How to Make It
Heat the oven to 450°. In a large deep frying pan, heat 1 tablespoon of the oil over moderate heat. Add the sausages and cook until browned and cooked through, about 10 minutes. Remove. When the sausages are cool enough to handle, cut them into 1/4-inch slices.
Add the remaining 1 tablespoon oil to the pan and heat over moderately low heat. Add the onion, fennel bulb, garlic, and fennel seeds and cook, covered, for 5 minutes. Stir in the potatoes and salt and cook, covered, until the vegetables start to soften, about 5 minutes.
Stir in the wine and simmer until evaporated. Stir in the tomatoes. Raise the heat to moderately high and simmer until no liquid remains in the pan, 2 to 3 minutes longer. Stir in the sausages and transfer the mixture to a 9-by-13-inch baking dish.
Bake the sausage mixture for 10 minutes. Remove from the oven and top with the fontina. Bake until the vegetables are tender and the cheese is melted, about 10 minutes longer.