Melt butter in a large nonstick skillet over medium-high heat. Add onion; sauté 5 minutes or until tender. Add sage, 1/4 teaspoon salt, 1/8 teaspoon pepper, and mushrooms; sauté 5 minutes or until mushrooms begin to brown. Spoon mixture into a large bowl.
Combine 1/4 cup flour and paprika in a shallow dish. Cut each chicken breast half in half lengthwise; cut crosswise into 1/4-inch strips. Dredge chicken strips in flour mixture; shake off the excess flour mixture. Heat oil in pan over medium-high heat. Add chicken; sprinkle with 1/4 teaspoon salt and the remaining 1/8 teaspoon pepper. Sauté 4 minutes or until chicken is done. Add chicken to mushroom mixture.
Add broth and sherry to pan, scraping pan to loosen browned bits. Reduce heat to medium-low. Place sour cream in a small bowl; sprinkle with 1 tablespoon flour. Stir with a whisk until combined. Stir sour cream mixture and remaining 3/4 teaspoon salt into broth mixture. Stir in chicken mixture; cook 1 minute or until thoroughly heated. Add noodles and parsley; stir well to combine.