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1
Bring 4 quarts water to a boil in a large pot for the pasta.
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2
Meanwhile, heat 1 tablespoons of the butter in a 12-inch nonstick skillet over high heat until beginning to brown.
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3
Add the chicken, break up any clumps, and cook without stirring until beginning to brown, about 1 minute.
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4
Stir the chicken and continue to cook until almost cooked through, about 2 minutes longer.
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5
Transfer the chicken to a medium bowl, cover with foil, and set aside.
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6
Add 1 tablespoons more of the butter, the leek, and 1/4 teaspoons salt to the skillet and cook over high heat until browned on the edges, 2-3 minutes.
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7
Stir in the garlic, thyme and flour and cook until fragrant, about 30 seconds.
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8
Add the chicken broth and wine, bring to a simmer, and cook over medium heat until the sauce has thickened slightly and reduced to 1 1/4 cups, about 15 minutes.
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9
Meanwhile, stir 1 tablespoons salt and the asparagus into the boiling water and cook, stirring often, until the asparagus are crisp-tender, about 1 minute (do not overcook).
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10
Using a slotted spoon, transfer the asparagus to a paper towel-lined plate and set aside.
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11
Return the water to a boil, stir in the pasta, and cook, stirring often, until the pasta is al dente.
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12
Reserve 1 cup of the pasta cooking water, then drain the pasta and return it to the pot.
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13
Return the chicken to the skillet along with the remaining 2 tablespoons butter, the Parmesan, lemon zest and lemon juice.
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14
Continue to simmer until the chicken is cooked through, about 1 minute.
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15
Pour the chicken and sauce mixture over the pasta and add the asparagus and basil.
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16
Toss gently to combine, adding the reserved pasta cooking water as needed to loosen the sauce.
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17
Season with salt and pepper to taste and serve, passing additional Parmesan separately.
