Step 1

Add water to a large pan and bring to a simmer. Rinse any ice glaze from frozen Alaska Pollock under cold water. Turn off heat and gently add seafood to pan. Return heat to a simmer. Once simmering, cover pan and cook 4 to 5 minutes for frozen seafood or 2 minutes for fresh/thawed fish. Turn off heat and let seafood rest for 5 minutes or until seafood is opaque throughout; drain.

Step 2

Meanwhile, heat broiler/oven to medium-high (450oF). Place four individual gratin dishes, or one large shallow baking dish, in the lower part of the oven to warm.

Step 3

To make the sauce, put the milk, butter and flour into a nonstick saucepan. Heat, stirring constantly with a small whisk, until the sauce thickens. Remove from the heat and add half the cheese, stirring until melted. Add the mustard; season with salt and pepper.

Step 4

Remove Alaska Pollock fillets from poaching liquid; break into large chunks and place in the warm dishes. Pour the sauce over the fish. Sprinkle with bread crumbs and rosemary sprigs; add remaining cheese over the top.

Step 5

Broil for 3 tor 4 minutes, until browned and bubbling. Garnish with extra rosemary, if desired.