Place 2 ½ cups all-purpose flour and 1 teaspoon kosher salt in a large bowl and stir to combine. While stirring constantly with a wooden spoon or chopsticks, pour ¾ cup boiling water over the flour mixture a little bit at a time. Continue stirring until combined.

Add 2 tablespoons cool water onto the dry pockets of flour and knead the dough with your hands until a shaggy dough forms and the sides of the bowl are clean, 2 to 3 minutes. Knead in more cool water a teaspoon at a time as needed if it’s too dry.

Transfer the dough onto a work surface. Knead until the dough is smooth, about 4 minutes. Drizzle a little vegetable oil onto your hands and use it to coat the dough ball. Return the dough to the same bowl it was kneaded in. Press a sheet of plastic wrap directly onto the surface of the dough and let rest at room temperature for at least 1 and up to 2 hours, or refrigerate for up to 24 hours. Make the roux and cut the scallions when the dough is almost ready.

Place ½ cup all-purpose flour, ½ teaspoon kosher salt, ¼ teaspoon five-spice powder if using, and ¼ teaspoon MSG if using, in a small heatproof bowl. Stir until evenly combined.

Heat ¼ cup melted lard, vegetable oil, or peanut oil in a small skillet over medium heat until 400ºF or a tiny bit of flour sprinkled in sizzles immediately. Pour the oil over the flour mixture and stir to combine until all the flour is hydrated and a paste is formed. Set aside to cool for a few minutes. If the roux solidifies, reheat in the skillet over medium heat until loose, or microwave in 15-second intervals until melted into a liquid paste

Trim and halve 1 ½ medium bunches scallions lengthwise, then finely chop until you have 1 ¼ to 1 ⅓ cups.

Place 1 tablespoon of the neutral oil in a small bowl.

Divide the dough into 4 portions (about 130 grams each) and form each portion into a smooth ball. Working with 1 piece of dough at a time (keep the remaining pieces covered with plastic wrap), place in the bowl of oil and flip to coat until covered with a thin layer of oil. Place on a work surface (do not flour) and roll out into a rough, very thin rectangle (about 11x12-inches) with a longer side closer to you. If the dough is cold and hard to roll out, let sit for a few minutes before trying again.

Spread 1 ½ tablespoons of the roux evenly over the dough with your fingers. Sprinkle evenly with a quarter of the scallions (about ⅓ cup). Starting at the long side closest to you, roll tightly up into a thick rope and firmly press down to seal the seam. Position seam-side up, then roll the rope into a coil, tucking the tail end underneath the coil. Firmly press down to flatten until about ¾-inch thick and 3 ½ inches wide.

Repeat with the remaining dough balls, reserving the remaining oil in the bowl. Place on a plate or small baking sheet in a single layer. Cover with plastic wrap and let rest for at least 1 hour at room temperature or up to 24 hours in the refrigerator.

Place 2 tablespoons soy sauce, 1 tablespoon Chinese black vinegar, 1 ½ teaspoons chili oil if using, and ½ teaspoon granulated sugar in a small bowl and stir until the sugar is dissolved.

Heat a large (at least 12-inch) cast iron or nonstick skillet over medium heat until hot, at least 3 minutes. Meanwhile, dip your hands in the reserved oil and coat each dough patty with a thin layer of oil. Roll out one of the patties on a work surface (do not flour) until 8-inches wide and about ¼-inch thick.

Add 2 tablespoons of the neutral oil to the heated skillet and heat until shimmering. Add the pancake, cover, and fry until the bottom is golden brown and crisp, 2 to 3 minutes. Flip the pancake and fry uncovered until the second side is golden brown and crisp (drizzle a little more oil around the edges if the pan is dry), 2 to 3 minutes more. Meanwhile, roll out the next pancake.

Position 2 flat spatulas (or a spatula and chopsticks) vertically on opposite sides of the pancake in the skillet. Push the spatulas inward towards each other; this pushes the pancake up slightly to separate the flaky layers (it’s okay if it breaks apart a bit). Repeat pushing up the pancake in a few spots. Transfer to a wire rack (or place the rack on a baking sheet and keep warm in a 200ºF oven while you fry the remaining pancakes).

Repeat cooking the remaining pancakes, using 2 tablespoons neutral oil for each pancake. Pat any excess oil on the pancakes with a paper towel if desired. Cut into wedges and serve with the dipping sauce.