Preheat oven to 350 degrees. Wash spinach and remove stems before drying leaves between paper towels. Set aside. Spread pine nuts over bottom of sheet pan and place pan in oven on top rack. Roast until golden brown, approximately 2 to 4 minutes. Remove from oven and set aside. Peel and devein shrimp. Set aside. Wash and slice fresh mushrooms. Set aside. Boil pasta in large pot of water to al dente stage according to directions on package. Set Aside.
Prepare lemon butter sauce: Melt 1 tablespoon butter in large skillet over medium-high heat. Saute shallots and garlic until translucent. Add white wine and reduce slightly more than ½, whisking occasionally. Add cream and reduce by ½. Add lemon juice and reduce by ½. Add white pepper. Reduce heat to low. Add remaining butter 2 tablespoons at a time, whisking continuously after each addition to completely incorporate butter. Continue to simmer, whisking until sauce just coats spoon.
In large skillet over medium-high heat melt the 4 tablespoons of butter. Add garlic and saute until garlic is translucent. Stir in mushrooms, shrimp, and pine nuts. Saute several minutes or until shrimp are done and show color. Remove skillet from heat and gently stir in spinach. Place warm pasta on plate with shrimp mixture to the side. Pour lemon sauce over pasta, permitting a bit of sauce onto shrimp.