Stir-fry with beef, mushrooms, and chard

Ingredients:

• 450 g beef tenderloin, cut into 6 mm thick slices.
• 1 tbsp and 2 tsp cornstarch
• 1 tbsp and 2 tsp balsamic vinegar
• 3 teaspoons soy sauce
• 2 teaspoons light brown sugar
• 3 tbsp. l. olive oil
• 3 cloves garlic, thinly sliced
• 1/2 small red onion, thinly sliced
• 120 g mixed mushrooms, sliced
• 1 bunch Swiss chard, stems cut into 1/2-inch pieces, leaves shredded
• Coarse salt and freshly ground pepper
• Juice of 1/2 lemon
• Cooked rice, for serving (optional)

Preparation:

1. In a bowl, combine the beef, 1 tablespoon cornstarch, 1 tablespoon vinegar, and 2 teaspoons soy sauce. In another bowl, combine the brown sugar, 1/3 cup water, the remaining cornstarch, vinegar, and soy sauce; stir until completely dissolved.
2. Heat 1 tablespoon olive oil in a large nonstick skillet over high heat. Add the beef and cook, stirring occasionally, for 2 to 3 minutes. Transfer the beef to a bowl and wipe the pan clean.
3. Add 2 tablespoons olive oil to the skillet and heat to high. Add the garlic and red onion and cook, stirring constantly, for 2 minutes. Add the mushrooms, chard stems, 1/4 teaspoon salt, and pepper to taste; cook, stirring constantly, until the vegetables begin to soften, 4 minutes. Add the chard leaves and continue to cook, stirring constantly, until the leaves begin to wilt. Add the soy mixture and beef to the vegetables and cook until thickened, 1 minute. Add the lemon juice, salt, and pepper. Serve. stir-fry with rice.
   
   Nutritional value per serving (excluding rice): Calories 300; Fat 15 g; Protein 28 g; Carbohydrates 13 g.