Pollock with Mustard Crust on Potatoes

Ingredients

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• 800 g (1.8 lb) waxy potatoes washed, boiled in their skins
• 2 tbsp vegetable oil 1 tbsp for the dish, 1 tbsp for drizzling
• 0.5 tsp salt plus a pinch for the cooking water
• black pepper to taste
• 4 pollock fillets about 5 oz (150 g) each, fresh or thawed, skinless; cod also works
• 1 tbsp lemon juice
• 1 pinch salt
• 3 tbsp medium-hot mustard Dijon-style also works
• 60 g (2.1 oz) plain dry breadcrumbs
• 40 g (1.4 oz) butter softened
• 0.5 bunch flat-leaf parsley finely chopped

Method

1. Boil the potatoes in their skins in salted water for 18 to 20 minutes, until a knife still goes in with slight resistance. Drain, let them steam dry and cool a little, then cut them into 1/4-inch (5 mm) slices.
2. Heat the oven to 400 °F (200 °C) conventional, or 350 °F (180 °C) convection. Grease a baking dish, about 9 × 12 inches (22 × 30 cm), with 1 tablespoon of the oil.
3. Arrange the potato slices in the dish, overlapping like roof tiles, drizzle with the remaining oil, season with salt and pepper and bake for 10 minutes.
4. Pat the fillets thoroughly dry with paper towels, drizzle with the lemon juice and season with salt and pepper.
5. For the crust, work the softened butter, mustard, breadcrumbs and parsley into a spreadable paste.
6. Take the dish out, lay the fillets on the potatoes, spread the crust about 1/8 inch (3 mm) thick on top and press it down lightly. Bake for 12 to 15 minutes.
7. The fish is done when it flakes easily with a fork at the thickest point and the crust is golden brown, at a core temperature of about 140 °F (60 °C). If the crust is still pale, put the dish under the broiler for 2 minutes.

Tip: Do not boil the potatoes until fully soft. They keep cooking in the oven, and firm ones cut into cleaner slices.

Tip: Pat thawed fish especially dry and put the crust on only right before baking, or it turns soggy.