Cook pasta according to package directions; drain., In a large skillet, heat 1/2 tablespoon each butter and oil over medium-high heat. Saute 1 pound shrimp with 1/4 teaspoon pepper flakes until shrimp turns pink, 3-5 minutes. Remove from pan; repeat., In same skillet, combine marinara sauce and cream; bring to a boil over medium heat. Stir in spinach until wilted. Add pasta and shrimp; toss and heat through.