In a large skillet over medium heat, melt the butter and heat the olive oil. Cut the mushroom caps in half, and slice 1/4 inch thick. Cook mushrooms in the skillet 8 minutes, or until tender and lightly browned. Season with salt. Stir in the chicken broth and Boursin cheese. Reduce heat and simmer, stirring constantly, until well blended.
Bring a large pot of lightly salted water to a boil. Add shell pasta and cook for 5 minutes. Place the asparagus into the pot, and continue cooking 5 minutes, until the pasta is al dente and the asparagus is tender; drain. Toss with the mushroom sauce to serve.
