Place the beef in a large stockpot (You can choose to brown them beforehand). Top it with the rest of the ingredients for the 'beef' (except salt and pepper). Add in the herb bag.Over high heat, bring the liquid to boil. Once boiled, simmer covered on low for 45 minutes. Season the broth with salt and white pepper. Make it a tad saltier. We're not going to consume the liquid. We just want the flavor to penetrate the meat.Continue to simmer on low heat for another 2 hours or until meat is super soft.Remove meat from liquid and let cool. Shred or thinly slice and set aside. To make slicing easier, refrigerate overnight before slicing. Chilled meat is easier to slice thin. To reheat meat, dip sliced meat in hot broth or place them under the broiler until warm (brush sliced meat with broth to prevent drying).In a bowl, combine all the ingredients for the sauce. Mix well.Brush some sauce over scallion pancake. Top with sliced cucumber. Top that with meat. Brush another layer of sauce over meat. Carefully roll it, cut stuff pancake rolls in half and serve immediately.