A recipe from Gourmet Magazine. The mustard-herb butter gives a lemony pop to the meatiness of the fish, while the French green lentils add a unique texture that regular brown lentils just don't have. Posted for ZWT-8 France.
For mustard butter- stir together all ingredients with 1/4 teaspoons each of salt and pepper.
Bring lentils, water, and 3/4 teaspoons salt to a boil in a heavy medium saucepan, then reduce heat and simmer, uncovered, until lentils are just tender, 20-25 minutes. Remove from heat and let stand 5 minutes. Reserve 1/2 cup cooking liquid, then drain lentils.
While lentils cook, chop leeks, then wash. Cook leeks in butter in a heavy medium skillet over medium-low heat, stirring occasionally, until softened, 6-8 minutes.
Add lentils with reserved cooking liquid to leeks along with 3 tablespoons mustard-herb butter and cook, stirring, until lentils are heated through and butter is melted. Add lemon juice and salt and pepper to taste. Remove from heat and keep warm, covered.
Saute salmon while leeks cook. Pat salmon dry and sprinkle with 1/2 teaspoons salt and 1/4 teaspoons pepper. Heat butter in a large nonstick skillet over medium-high heat until foam subsides, then saute salmon turning once, until golden and just cooked through, 6-8 minutes total.
Serve salmon, topped with remaining mustard-butter, over lentils.