1. Process 2 cups flour and baking powder in a food processor. With motor running, add ⅔ cup cold water; process until dough forms, about 40 seconds. Transfer to a plate; set aside. Add remaining flour and salt to food processor, and with motor running, add ⅔ cup boiling water; process until dough forms, about 30 seconds. Return reserved dough to food processor; pulse until both doughs come together, about 35 seconds. Transfer to a lightly floured work surface; knead until smooth, about 4 minutes. Transfer to a greased bowl, cover; let sit at room temperature for 2 hours.
2. Halve dough; using a rolling pin, roll 1 dough half into a 10" x 20" rectangle. Brush with 1 tbsp. canola oil and half the sesame oil. Sprinkle with half the scallions, half the chile flakes, and half the white pepper. Beginning with one long side, tightly roll dough like a jelly roll. Cut roll crosswise into 3 pieces, slightly stretch each piece, and starting from one edge, coil piece horizontally, tucking the end underneath. Using your hand, gently flatten coil into a disk; using a rolling pin, flatten into a 5" circle. Repeat with remaining pieces and second dough half, 1 tbsp. canola oil, remaining sesame oil, scallions, chile flakes, and white pepper. Let pancakes sit for about 10 minutes.
3. Heat oven to 200°. Heat 2 tsp. canola oil in a 10" nonstick skillet over medium heat. Add 1 pancake to skillet; cook, swirling skillet and turning once, until golden and crisp, about 10 minutes. Transfer to a baking sheet; place in oven to keep warm. Repeat with remaining oil and pancakes; cut into wedges to serve.