Preheat the oven to 350°F (177°C). Line a rimmed baking sheet with parchment paper. Bring a large pot of salted water to a boil.
Scatter the walnuts on the baking sheet and roast until fragrant and lightly browned at the edges, 7 to 10 minutes.
Immediately transfer the walnuts to a cutting board and let cool before coarsely chopping them.
Meanwhile, in a large skillet over medium-high heat, melt the butter. Add the sausage and cook, breaking up the meat with a spatula, until browned and no trace of pink remains, 8 to 10 minutes.
Cook the pasta in the boiling water, stirring often, until al dente, about 2 minutes less than the package instructions. When the pasta is done, drain it, reserving at least 1/2 cup pasta cooking water.
Add the cheese and half-and-half to the sausage, crank the heat to high, and boil, stirring often, until the half-and-half thickens a bit, 3 to 4 minutes.
Carefully dump the drained pasta into the skillet, reduce the heat to low, and simmer, tossing constantly, until the pasta is cooked through and the liquid has thickened, about 3 minutes more. If desired, thin the sauce with some of the reserved pasta cooking water.
Taste the pasta and season with pepper and salt, if needed.
Divide the pasta among warm bowls and top with more blue cheese and the walnuts. Serve immediately.