2 tablespoons olive oil
1 pound chicken breast tenders, thinly sliced on an angle
Salt and pepper
1/2 stick butter
12 ounces cremini mushrooms, thinly sliced
2 shallots, finely chopped
4 cloves garlic, finely chopped
3 tablespoons flour
1/2 cup dry sherry or dry white wine
2 cups whole milk
1/2 cup chicken stock
1 teaspoon dry mustard
A little freshly grated or ground nutmeg
1/2 cup (a couple handfuls) grated Parmigiano-Reggiano
1 pound egg tagliatelle or linguine
1 cup shelled fresh spring or frozen peas (preferably organic), thawed
1/4 cup tarragon leaves, chopped
Bring a large pot of water to a boil for the pasta.
Heat a large, nonstick skillet over medium-high. Add the oil, two turns of the pan. Add the chicken and season with salt and pepper. Cook, stirring occasionally, until lightly browned, about 3 minutes per side; transfer to a plate.
Add the butter to the skillet. When it melts, add the mushrooms and cook, stirring often, until lightly browned, about 2 minutes; season with salt and pepper. Add the shallots and garlic. Cook, stirring often, until the shallots soften, 2-3 minutes. Sprinkle with the flour and stir to combine. Whisk in the sherry and cook, stirring often, until reduced by half, about 1 minute. Add the milk and stock, and boil, stirring occasionally, until the sauce thickens, about 8 minutes. Add the dry mustard and a little sprinkle of nutmeg to the sauce; stir in the cheese and season. Return the chicken to the skillet; reduce the heat to low.
Salt the boiling water, add the pasta and cook to almost al dente. Reserve 1/2 cup of the starchy cooking water, then drain the pasta.
Add the peas and tarragon to the sauce and return to a bubble. Toss in the pasta, adding some of the reserved starchy cooking water to loosen if the sauce is too thick. Serve in shallow bowls.