Prepare Balsamic Reduction with Wild Mushrooms. Add beef mixture to pan; cook 2 minutes until beef and mushrooms are heated through.
Balsamic Reduction with Wild Mushrooms: Bring 1/2 cup balsamic vinegar to a boil in medium saucepan. Reduce heat; simmer 8 to 9 minutes until reduced to 2 tablespoons (consistency will be syrupy). Set aside to cool. In same skillet used to prepare beef and mushrooms, heat 1 tablespoon olive oil over medium heat until hot. Add 4 ounces minced wild mushrooms; cook and stir 5 to 8 minutes until mushrooms are lightly browned. Add 4 teaspoons minced garlic; cook and stir 2 minutes. Add 1/2 cup dry red wine; cook 2 to 5 minutes until liquid is completely evaporated. Dissolve 1 tablespoon cornstarch in 1 can (14 to 14.5 ounces) reduced-sodium beef broth. Add broth mixture and balsamic vinegar reduction to skillet; bring to a boil, stirring constantly. Reduce heat; simmer 15 to 20 minutes until mixture is reduced by half. Add in 1 tablespoon butter; stir until melted.