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bring a large pot of salted water to a boil for the pasta.
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put the butter in a medium skillet over medium-low heat.
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as it melts, crumble the sausage meat into it, making the bits quite small, 1/2 inch or less.
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add the liquid and adjust the heat so that the mixture simmers gently.
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cook the pasta until it is tender but not at all mushy.
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reserve about 1/2 cup of the pasta cooking water.
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drain the pasta, and dress with the sauce, adding a little of the reserved cooking liquid if necessary.
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toss with salt, pepper and parmesan, and serve.