Finely mince the Chinese bacon and toast in a skillet on medium high heat until the fat has rendered and the bacon pieces are crispy. Set aside and let cool. You can use the rendered bacon fat in the skillet for the crepes.
Make the crepe batter: mix together sourdough discard, water, salt, and cornstarch. Set aside.
Make the egg layer: scramble egg with a splash of water and salt. Mix in scallion. Set aside.
Heat up the skillet with the rendered bacon fat on medium high heat. Pour half of the batter into the pan and quickly lift the skillet at an angle and rotate it around so the batter creates an even thin layer. When the top starts setting (it will start looking translucent), mix your egg layer again and pour half of it on top of the crepe layer. Lift and rotate your skillet to create another even thin layer. Sprinkle half of the toasted bacon on top.
Optional: When the egg layer sets, carefully flip the crepe so the egg layer is on the bottom. This will be very quick ~10 seconds. Flip the crepe so the egg side is back on top.
Using a spatula or chopsticks, roll up the crepe. Alternatively, you can transfer the crepe onto a cutting board and roll it up there. Repeat with the other half. To create thicker crepe rolls you can put the first crepe roll on top of second before rolling it up.
Make the dipping sauce: mix together soy sauce, black vinegar, ginger and sesame seeds.
Cut and serve warm with dipping sauce.