Combine flour and salt in a bowl. Add the egg and gradually add warm water, mixing until a firm dough forms.
Knead for 8 to 10 minutes until smooth. Cover and rest for 30 minutes.
Combine ground beef, grated onion, salt, pepper and optional red pepper flakes.
Divide the dough into 3 or 4 portions. Keep unused portions covered.
Roll one portion thinly, approximately 1 mm thick, and cut into 3 cm squares.
Place a small amount of filling in the center of each square.
Bring the four corners together and pinch firmly to seal.
Boil the mantı in salted water for 8 to 12 minutes, until tender and cooked through. Reserve a little cooking water.
Mix yogurt with garlic and salt.
Melt butter, stir in tomato paste and paprika, then loosen with reserved cooking water.
Serve hot mantı topped with garlic yogurt, butter sauce, dried mint and sumac.