Cook onions:
Melt 1 1/2 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.