Mix flour and salt in large bowl. Allow boiling water to cool for 1 minute. Using wooden spoon, slowly stir in 1/3 cup hot water until a ball is formed and all the flour is incorporated. If any flour remains at bottom of bowl, drizzle in hot water 1 tsp at a time, and continue to stir until all flour is incorporated. Place dough on lightly floured surface and knead until smooth and elastic, 3-5 minutes. Add flour as necessary to keep dough from sticking. Place dough back in bowl, cover with a damp cloth and allow to rest for 30-60 minutes. Dough may be made one or two days in advance and stored lightly oiled and tightly wrapped in plastic. Bring to room temperature before using.
When ready to form pancakes, cut the dough into 4 equal pieces. Take 1 piece and cover the remaining pieces with a damp cloth. Roll the piece into a ball, flatten it slightly then use a rolling pin to flatten it into a circle about 8 inches in diameter. Brush the circle with 1 Tbsp sesame oil then sprinkle with 1/3 cup scallions. Roll up the circle into a snake then twist the snake into a snail-like spiral and tuck the ends underneath. Flatten slightly with your hands then use the rolling pin to roll out again into an 8 inch circle. You may stop here or repeat the steps to create more flaky layers. Repeat this process with the remaining 3 balls of dough.
To cook the pancakes, heat a layer of oil in a large skillet over medium high heat until shimmering. Carefully slide the pancake into the pan and fry on each side until golden brown, about 3 minutes per side. Sprinkle lightly with salt and place on a paper towel to cool. Repeat with remaining dough discs.
Put the egg yolk, garlic, 1 1/2 Tbsp soy sauce and 1 Tbsp rice vinegar in a sturdy medium bowl and whisk to combine. Very slowly drip in the oil while whisking vigorously. Continue until mixture is thickened and well emulsified. After about 1/2 of the oil has been incorporated, the remaining oil may be whisked in more quickly. Whisk in remaining 1/2 Tbsp soy sauce and 1/2 Tbsp vinegar.
Layer 4 slices bacon and two slices tomato on one scallion pancake. Drizzle with Soy Aioli. Top with mixed greens and fold the pancake in half. Cut in half and serve immediately.
Recipe by Irene Li, Mei Mei, Boston