Combine the beef, pork, club soda, salt, garlic, pepper, baking soda and bread in a mixing bowl and mix together by hand for at least 5 to 10 minutes. Refrigerate, covered, for a few hours or up to 12 hours.
Grab a small handful of the meat mixture and roll between your hands to form breakfast sausage-size links. Repeat with the remaining meat.
Heat a griddle
until hot. Lightly grease
the griddle with some oil, and then cook the cevapcici, rolling them around occasionally, until cooked though and golden.
To serve: Grill
the cut sides of the rolls. Sandwich the cevapcici and onions
in the rolls with dollops of Kajmak and avjar and serve.