Easy Fish Gratin Recipe

Preheat the oven to 180C/160CFan/360F.
Place the butter into a small saucepan over medium-high heat and allow to melt. Add the sliced leeks and sauté gently for 15 minutes.
While the leeks are cooking make the cheese sauce. Pour the double cream into a small saucepan and heat up gently over medium heat, stir through the mustard.
Mix the cornflour with a little water to make a paste and add that to the warm cream and keep stirring until the cream thickens to a sauce.
Now add 100g (approx 1 cup) of the cheddar cheese to the sauce, setting the remaining cheese aside. Keep stirring until the cheese has melted, season with salt and black pepper then take off the heat.
Layer the cooked leeks into the bottom of the baking dish, place the fish fillets on top and scatter the cherry tomatoes and garden peas around the fish.
Pour over the cheese sauce over the fish. Mix the remaining cheese with the breadcrumbs and spread over the top of the dish.
Place the fish into the hot oven and bake for 20-25 minutes if using fresh fish, 30-35 minutes for frozen fish, until the fish has reached an internal temperature of 63C/145F.
Note - cooking times will vary depending on the size and thickness of the fish used.
Remove from oven and serve immediately.