Beef & Potato Empanadas

Ingredients

• 1/2 cup unsalted butter (frozen)
• 2 1/4 cups all purpose flour
• 2 teaspoons salt
• 1 large egg
• 1/3 cup cold water
• 1 1/2 tablespoons white vinegar
• 1 tablespoon olive oil
• 1/2 baking potato (large, diced into 1/4-inch cubes)
• 1/2 white onion (small, diced)
• 1/2 red pepper (cored and diced)
• salt
• pepper
• 1 pound ground beef
• 15 cherry tomatoes (halved)
• 1 clove garlic (diced)
• 1/2 bunch cilantro (minced)
• 1 large egg
• 2 tablespoons milk