In a large mixing bowl, add the flour and slowly pour in the boiling water while stirring continuously with a wooden spoon or chopsticks. Gradually add the cold water until the dough starts to come together. Transfer the dough onto a floured surface and knead for about 5-7 minutes until smooth and elastic. Cover with a damp cloth and let it rest for 30 minutes to relax the gluten.

Divide the rested dough into 4 equal pieces. On a lightly floured surface, roll each piece into a thin circle approximately 8 inches in diameter, preparing them for filling.

Lightly brush each dough circle with sesame oil if using, or vegetable oil as a substitute. Evenly sprinkle the finely chopped scallions over the dough and add a pinch of salt to enhance the flavor.

Roll each dough circle tightly into a log, then coil it into a spiral shape. Gently flatten the spiral with your hand and roll it out again carefully into a thin pancake about 6 inches in diameter, ensuring the scallions are distributed inside.

Heat 1-2 tablespoons of vegetable oil in a large skillet or frying pan over medium heat. Place each pancake in the skillet and cook for 2-3 minutes on each side until golden brown and crispy. Add more oil as needed for the remaining pancakes.

Cut the cooked pancakes into wedges and serve hot. These scallion pancakes are delicious on their own or paired with dipping sauces like soy sauce, black vinegar, or chili oil for extra flavor.