French Onion Pierogy Soup - Mrs. T's Pierogies

Ingredients

• 1 box Mrs. T’s Classic Onion Pierogies
• 3 tablespoons butter
• 3 tablespoons olive oil, divided
• 2 pounds yellow onion, thinly sliced
• 1 teaspoon salt
• ¼ cup dry white wine
• 2 tablespoons garlic, finely chopped
• 2 tablespoons flour
• 1 tablespoon tomato paste
• 4 cups beef broth
• 2 cups shredded mozzarella cheese