Cook onions: Melt 1 ½ tablespoons of the butter in a large saucepan or Dutch oven over low. Add the onion, and sauté 3 to 4 minutes or until softened.
Add flour: Add remaining butter; stir until melted. Add flour; stir and cook until onions are coated, about 1 minute.
Add remaining ingredients: Stir in the milk until blended. Stir in the crabmeat and roe (or yolk); add pepper and mace, and cook 20 minutes. Stir in the half-and-half until heated through. Remove from heat, and stir in the wine and salt. Serve warm, garnished with a sprinkle of paprika, fresh parsley, and additional roe (or yolk) if desired.
