Hake with lentils and sage mustard butter

In this take on the classic French recipe Saumon aux Lentilles, mild white-fleshed fish and sage stand in for salmon and tarragon.

Blue Kitchen
Hake served with lentils and sage mustard butter.

Julia Child famously said, “If you’re afraid of butter, use cream.” We’re not afraid of butter. We use an impressive amount, especially given how little we bake. But when I started researching the classic French dish of salmon with lentils and mustard-herb butter, I was still taken aback by how much butter was called for.

Strictly speaking, it wasn’t just the volume of butter – eight tablespoons, a stick of butter, divided among the various components. It’s that this dish was fish. And lentils. These are not foods one generally associates with such exuberant use of butter. 

So I flinched. I reduced the total butter for all moving parts to a mere five and a half tablespoons, adding in a little olive oil. The results were still amazing, proving once again the velvety wonderfulness of butter and how the French, better than perhaps anyone, understand how to exploit its rich flavor and mouth feel.

The dish also reminds me that the kind of French cooking (and eating) I enjoy most actually revolves around simple, well chosen ingredients and equally simple techniques. The sage mustard butter is a perfect example – softened butter, fresh sage and parsley, whole grain mustard, lemon juice, salt and pepper mixed together in a bowl. That’s it. The result is bright, tart and lively, with a creamy undercurrent. There is no big ballpark hot dog mustard blast here; in fact, there is no signature mustard taste at all. Suffice it to say that cleaning up after dinner involved a certain amount of spatula licking – a grownup version of licking the cake batter spoon.

At least in part due to the sage mustard butter, the lentils are a star in their own right, a show-stealing side dish with or without the fish. Speaking of the fish, I swapped mild tasting hake for the more traditional salmon. Partly, I wanted a less assertive fish for the meal. And partly, with cold weather stubbornly hanging on, I didn’t want to be smelling salmon for days in our apartment. Cod, haddock, halibut, pollock and tilapia would also work.

Hake with Lentils and Sage Mustard Butter
 Serves 4

For sage mustard butter:

4 tablespoons unsalted butter, softened

1-1/2 teaspoons chopped fresh sage

1-1/2 teaspoons chopped fresh Italian parsley

2 teaspoons whole grain mustard

2 teaspoons fresh lemon juice

rounded 1/8 teaspoon each, salt and freshly ground black pepper

For lentils:

1 cup lentils

4 cups water

3/4 teaspoon salt

2 medium leeks (white and pale green parts only)

1 tablespoon unsalted butter

olive oil

3 tablespoons sage butter

1 tablespoon lemon juice

For fish:

4 4-1/2 to 6-ounce hake loins or fillets (or cod or other mild white-fleshed fish)

Salt and freshly ground black pepper

1-1/2 tablespoons olive oil

1/2 tablespoon unsalted butter

Make the sage mustard butter. Thoroughly mix all ingredients in a bowl. Set aside. Sage mustard butter can be made a day ahead and kept in the fridge in an airtight container. Let come to room temperature for an hour before using.

Make the lentils. Combine lentils, water and salt in a medium saucepan. Bring to a boil over medium-high heat. Reduce heat and simmer, uncovered, until lentils are just tender, about 20 minutes or so. Reserve 1/2 cup cooking water (most of the water remaining) and drain. Set aside.

Meanwhile, trim leeks and halve lengthwise. Rinse under cold running water, fanning to wash away any grit. Slice into half moons. Melt butter in a medium sauté pan or skillet over medium-low flame. Sweat leeks, stirring occasionally, for 6 to 8 minutes. Drizzle in some olive oil if the pan seems dry.

Add lentils, reserved cooking water and 3 tablespoons sage mustard butter to the pan and cook until warmed through, stirring occasionally. Remove from heat, cover and keep warm.

Cook the fish. Pat fish dry with paper towels and season with salt and pepper. Heat a large nonstick skillet over medium flame. Add oil and butter, swirling pan to combine. Add fish and cook for 3 to 4 minutes, until lightly browned. Turn and cook until just cooked through, another 2 to 3 minutes.

Plate the dish. As fish is finishing, divide lentils among four shallow bowls. Top with fish. Top fish with dollops of remaining sage mustard butter. Serve.

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