Creamy Cod and Leek Potato Gratin 8 Steps
Place the salted cod fillets in cold water and soak in the fridge for 24 hours, changing the water twice throughout. It may be necessary to soak the cod for 36 hours if they are quite thick. When ready to use, drain and allow to dry on paper towel, then cut into 1 cm thick strips and set aside until ready to assemble.
Split the leek in half lengthwise and run under water separating each layer to remove any dirt, dry and then cut into 1/4 inch slices (you should have approximately 4 cups). Heat a saute pan on low heat and melt the butter, add in the sliced leeks as well as a light sprinkle of kosher salt and cook for about 10-12 minutes until the leeks have softened, stirring regularly. Set aside until ready to assemble.
In a small sauce pot, heat the heavy cream with the rasped garlic cloves until just warm.
Peel and slice the russet potatoes about 2-3 mm thick and get ready to assemble the gratin.
In a 2-3 quart casserole dish, layer 1/3 of the sliced potatoes in a scalloped and slightly overlapping pattern and season lightly with kosher salt as well as black pepper. Top the potatoes with an even layer of 1/3 of the sliced cod, using your fingers to gently flake into bite sized piecess. Follow with an even layer of the cooked leeks and then with 1/3 of the warmed cream and garlic mixture. Repeat this process 2 more times (3 layers in total).
Cut a piece of parchment paper the same approximate size as the casserole dish, place this right on top of the layered potatoes, then wrap well with aluminium foil and bake in a preheated 350°F oven for 45 minutes.
After 45 minutes, remove the foil as well as parchment paper and continue to bake uncovered for another 45 minutes or until the sauce is bubbly, top is golden brown and the potatoes are cooked through.
Top with some chopped parsley and allow the potato gratin to set for 15-20 minutes prior to serving to avoid a runny mess.