Fill a large pot with water, add a generous pinch of salt, and bring it to a rolling boil. Add your pasta and cook according to the package instructions until al dente. Reserve about ½ cup of pasta water before draining, then drain the pasta in a colander.
While the pasta cooks, heat a dry skillet over medium heat. Add the walnuts and toast them, stirring frequently, until they are golden and fragrant—about 3-5 minutes. Remove from heat and set aside.
In the same skillet, pour in the heavy cream and bring it to a gentle simmer over medium heat. Add the chopped rosemary and stir for 1-2 minutes to infuse the cream with the herb’s flavor.
Lower the heat and stir in the room temperature blue cheese. Whisk gently until the cheese melts into the cream, creating a smooth sauce. If the sauce is too thick, add a splash of reserved pasta water to loosen it.
Add the drained pasta to the skillet with the sauce. Toss gently to coat every piece of pasta in the creamy blue cheese mixture. Add more pasta water if needed to achieve your preferred consistency.
Sprinkle the toasted walnuts over the pasta and give it one last gentle toss. Taste and adjust seasoning with salt if necessary.
Transfer the pasta to serving plates or a large bowl. Garnish with extra rosemary or a few more walnut pieces for presentation if you like. Serve immediately for the best flavor and texture.
