In a large frypan over medium heat, melt the butter and heat the olive oil. Cut the mushroom caps in half and slice 5mm thick. Cook mushrooms in the frypan 8 minutes, or until tender and lightly browned. Season with salt. Stir in the chicken stock and Boursin cheese. Reduce heat and simmer, stirring constantly, until well blended.
Bring a large pot of lightly salted water to a boil. Add cannelloni 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.