Mandu Korean Dumplings

Name: Mandu (Korean Dumplings)
Ingredients: 8 ounces medium-firm tofu; 8 ounces ground pork; 8 ounces ground beef; 2 cups buchu (Korean garlic chives ), finely chopped; 1/2 medium yellow onion , finely chopped; 3 cloves garlic , minced; 1 tablespoon fresh ginger , minced; 1 large egg; 1 tablespoon soy sauce; 1 tablespoon toasted sesame oil; 1 teaspoon salt; 1 teaspoon white or black pepper; Flour , for sprinkling; 1 package ( 50 to 60 wrappers) store-bought or homemade mandu wrappers; 2 tablespoons vegetable oil , for pan frying; 4 tablespoons soy sauce; 4 tablespoons rice vinegar; 1 scallion , trimmed and thinly sliced; 1 clove garlic , minced; 1 teaspoon sesame oil; 1 teaspoon toasted sesame seeds; 1/2 teaspoon gochugaru (Korean chili flakes ), optional