Thaw shrimp, if frozen. Rinse shrimp; pat dry with paper towels. In a Dutch oven, cook pasta according to package directions; drain. Return to Dutch oven; cover and keep warm.
Meanwhile, in a small bowl, combine 3/4 cup chicken broth, the sherry or additional broth, lemon juice, crushed red pepper, and salt; set aside. In a large skillet, cook shrimp, 1/4 cup pine nuts, and the garlic in hot oil over medium heat for 2 to 3 minutes or until shrimp are opaque. Remove shrimp mixture from skillet.
Add mushrooms and butter to skillet; cook about 3 minutes or until nearly tender. Carefully add broth mixture to skillet. Bring to boiling; reduce heat. Boil gently, uncovered, for 5 minutes. Return shrimp mixture to skillet; heat through.
Add shrimp mixture and the spinach to pasta; toss to combine. Transfer to a serving bowl. Sprinkle with Asiago cheese and, if desired, toasted pine nuts. Makes 4 servings.