I have watched my mom prepare rouladen many times, and I'm sure I've even helped in the past. But, this is the first time I made them on my own (aside from Rachael's thread wrapping help).
Rouladen as I know it is made from beef. You can usually ask the butcher for rouladen cuts, and many butchers will already have it pre-cut (especially the Freybe Outlet Store on Hastings just off Victoria Drive). You don't pound it flat or anything - it comes cut as thin as you need it to be.
The quantities I mention here are for 16 rouladen. You want to figure about 2 per person and/or to have lots of leftovers, because they are delicious. Aside from the 16 strips of beef for the rouladen, you'll also need:
Mince the bacon and cook it over medium heat (or stick it in the oven) until it's nice and crispy. You'll want to drain the fat / juices as you go (save them!) to make sure it gets crispy. Mince the onions and saute them (perhaps with some of that delicious bacon juice) on low until translucent / tender. Mince the pickles. Once the bacon & onions are done, drain the fat / pat them to soak up some of the fat and let them cool. Once everything is no longer piping hot you can mix all of these things together.
Lay out the rouladen on a counter / workspace and spread with mustard. Do a twist of cracked pepper and salt over each piece of meat as well. Spoon on 2 Tbsp or soon onto one end of the piece of meat. Roll up the meat and secure it. If you're using thread, it's easiest if you do all the rolls, and then have someone help you wrap and tie each bundle.
Remember the bacon juice you saved? Put it in a pan and heat. Brown the rouladen on each side, doing them in batches until they are all browned. Place them in a dutch oven or casserole dish, sprinkling a little flour on them as you layer them in.
Deglaze the pan with water (or beer or wine) and pour over the dish of rouladen. Stir in a Tbsp or so of mustard for a bit more "tang" to the sauce as well as any leftover minced bacon / onion / pickle bits. Add water / liquor as needed so that the rouladen are mostly submerged. Cover and cook at 350°F for 45 minutes or so.
I made this for Lauren's birthday party. We ended up serving it as a "meatatizer" - it was lukewarm and we prepped it by cutting all the thread off and cutting it into slices. The cross section of the rolled meat with the stuffing looks nice on a plate.
Traditionally, you'd have this with potatoes or spätzle, plus some sort of highly cooked vegetable like red cabbage or perhaps some sauerkraut.