Best use thinly sliced veal or if not available, use thinrump steak.
Meat needs to be a large piece, thinly sliced and hammered out. Veal tastes better and doesn’t take as long to cook.
Hammer all meat and lay out in a row. Allow for finely chopped onion and bacon. Speck has a more smokey flavour but is only available at delis.
Spread German mustard, strong is better, such as Thomy mustard. Spread each slice reasonably with mustard. Pile up on the larger end the chopped bacon and onion, as much as possible. If it is a long slice, you can put onion down the whole slice. Roll up tightly and hold together with toothpicks.
Put a little oil (olive or butter) in a large pan and seal. (brown on all sides). This should only take a few minutes. When browned, add a little water or stock and cracked pepper and 1 tspn paprika, , put lid on, turn down heat and braise slowly (simmer). Veal may only take 40 mins but beef may take over an hour. Keep topping up with water (quarter cup at a time) but only a little at a time. If you add too much water you are actually boiling the meat which toughens the meat and loses flavour.
Let stock reduce and serve Rouladen as is.
Alternatively you can add cream to the stock just before serving, thicken with a little cornflour (dissolved in water)
You can always add sliced mushrooms or even red wine to the stock for flavour.