I began making this dish years ago when I was cooking in Los Angeles. And it was a favorite among my catering guests. The smell of the crusty, fresh horseradish topping combines with the delicate onion aroma of the chive mashed potatoes and a delectable crème fraîche sauce to evoke a favorite childhood comfort food: a bag of sour cream and onion potato chips. Your whole house will smell great when you cook it! Use a food mill or ricer to achieve fluffy, creamy mashed potatoes. Also note, when topping the fish with the bread crumb mixture, don’t feel obligated to pile every last crumb on there. You will make a generous amount of horseradish mixture, so use it all if you like, or use less. I always think that it’s better to have it and not need it, then need it and not have it. Any extra can be toasted in a pan for use on a salad the next day.
SERVES 4
Chive Mashed Potatoes
2 lb [910 g] Idaho potatoes, peeled and quartered
Kosher salt
1/2 cup [25 g] roughly chopped chives, plus more for garnish if desired
2/3 cup [160 ml] extra-virgin olive oil
1 cup [240 ml] half-and-half
3 Tbsp butter
Freshly ground black pepper
3 Tbsp whole milk (if reheating the potatoes), plus more as needed
Topping for Fish
1 small horseradish root, peeled and roughly chopped (its odor is strong and will clear your airways!)
2 Tbsp butter
1 cup [60 g] panko bread crumbs
2 tsp kosher salt
2 Tbsp finely chopped fresh Italian parsley leaves
Four 6 oz [170 g] cod fillets
Freshly ground black pepper
Lemon Crème Fraîche Sauce
1/4 cup [60 g] crème fraîche
1/4 cup [60 ml] store-bought veal demi-glace
2 Tbsp fresh lemon juice
To make the chive mashed potatoes: Place the potatoes in a large pot, season generously with salt, and cover with cold water by at least 1 in [2.5 cm]. Cover and bring to a boil over medium-high heat, remove the lid, lower the heat to a simmer, and cook until the potatoes are fork tender but still offer a bit of resistance (you don’t want them falling apart), about 12 minutes.
Meanwhile, in a blender, combine the chives and olive oil and blend to make a smooth purée, about 20 seconds. Set aside.
Drain the potatoes in a colander. Set a ricer (or food mill) over the now-empty potato pot and rice the potatoes, so that they fall in a fluffy mound back into the pot.
In a small saucepan over medium-low heat, combine the half-and-half and butter and slowly heat until the butter is melted. Add the mixture to the pot of riced potatoes and gently fold it in, using a rubber spatula (or the back of a wooden spoon) so that the potatoes absorb it all and get good and creamy. Taste for seasoning and add more salt and pepper. Add the chive purée and mix well to achieve uniform fresh, bright green colorful specks throughout the mashed potatoes. Cover to keep warm and set aside.
Preheat the oven to 425°F [220°C].
To make the cod: In a blender, combine the horseradish, butter, bread crumbs, salt, and parsley and blend for 10 seconds until it is well combined and finely crumbled. If it needs an extra pulse or two, go for it. Set aside.
Line a baking sheet with aluminum foil and rub it with 2 Tbsp butter to prevent the fish from sticking. Place the cod on the baking sheet, generously season with salt and a few grinds of pepper, and top with the horseradish mixture, patting it down so that it sticks and makes a crust. Bake until the horseradish topping is golden brown and the fish is opaque and flakes nicely when you poke it with a fork, 7 to 8 minutes, depending on the thickness of your fillet.
Meanwhile, prepare the lemon crème fraîche sauce: In a small saucepan over medium-low heat, add the crème fraîche, demi-glace, and lemon juice and whisk to combine. As soon as it comes to a boil, cover and set aside.
If you made the potatoes ahead of time, you can reheat them in a saucepan over low heat, adding 3 Tbsp of whole milk (or more), as needed, to help thin them out until they are heated through. Or not. (Sometimes they need it and sometimes they don’t, especially if they are perfectly creamy; I trust you to make that call.)
Divide the chive mashed potatoes among four plates, top with generous spoons of sauce, place the cod fillet on top, and while you’re add it, snip some more fresh chives for a nice touch! Serve immediately.
