Trim fat from tenderloins. Combine flour and pepper in a shallow bowl; dredge tenderloins in flour mixture. Cook tenderloins, uncovered, in hot oil in a large skillet over medium heat 10 minutes, turning occasionally. Insert meat thermometer into thickest part of tenderloin, if desired. Cover and cook an additional 20 minutes or until meat thermometer registers 160°. Transfer tenderloins to a serving platter, and keep warm.
Melt 2 tablespoons butter in a large saucepan; add mushrooms, and cook 5 minutes. Add brandy and chicken broth. Bring to a boil, and cook over medium-high heat until mixture is reduced by half, stirring occasionally. Stir in whipping cream, and cook over medium-high heat 10 to 15 minutes or until mixture thickens. Remove from heat; add remaining 2 tablespoons butter, mustard, and sage, and stir with a wire whisk.
To serve, cut tenderloins diagonally across grain into thin slices, and serve with cream sauce.