Place the fish in a deep sided baking dish, 9 x 6 inch. Evenly spread over the onion and set aside.
In a large sauce pan set over medium to high heat, add the butter and garlic until it sizzles. Add the flour and stir quickly and continue to stir for a few minutes. Start gradually adding the milk and whisking as it thickens. Continue this until all the milk has been added and you have a thick sauce.
Add the mustard, tarragon, salt, pepper and parmesan cheese. Stir well and remove from heat.
Pour the sauce over the fish.
In a large bowl, combine the bread crumbs with the cheddar cheese and chives. Mix well. Sprinkle over the fish.
Bake for about 45 minutes or until fish is completely cooked and the top is golden. Let sit for about 10 minutes before serving.
*A note on times provided: appliances vary, any prep and/or cook times provided are estimates only.
Nutrition Facts
Cod au Gratin
Amount Per Serving (1 serving)
Calories 380Calories from Fat 135
% Daily Value*
Fat 15g23%
Saturated Fat 9g56%
Cholesterol 104mg35%
Sodium 513mg22%
Potassium 799mg23%
Carbohydrates 20g7%
Fiber 1g4%
Sugar 5g6%
Protein 39g78%
Vitamin A 531IU11%
Vitamin C 2mg2%
Calcium 353mg35%
Iron 2mg11%
* Percent Daily Values are based on a 2000 calorie diet.