Pie Will Never Be the Same After This Ground Beef and Cheese Version

Ingredients

• 1 Tbsp. extra-virgin olive oil
• 1 small onion, finely diced
• 1 medium Yukon Gold potato, peeled and cut into 1/4-inch cubes
• Kosher salt and freshly ground black pepper
• 2 lb. ground beef
• ¼ cup white wine vinegar or fresh lemon juice
• 2 large cloves garlic, finely chopped
• 8 oz. provolone, shredded
• ½ bunches broccoli rabe, trimmed and cut into ¾-inch pieces (2 cups or 3 oz.)
• Crushed red chile flakes
• 2 sheets frozen all-butter puff pastry, thawed in the refrigerator for at least 3 hours
• All-purpose flour, for dusting
• 1 large egg, beaten with 1 tsp. water