In a large, deep skillet, heat the remaining 2 tablespoons of oil until shimmering. Add the fennel and onion and cook over moderately high heat, stirring, until softened, 7 minutes. Add the garlic, orange zest and ground cloves and cook until fragrant, 1 minute. Add the wine and cook until nearly evaporated, 5 minutes. Add the clam juice, tomatoes, saffron and 1 cup of water and bring to a boil. Season with salt and pepper and simmer until the sauce is reduced by half, 10 minutes.