Preheat your Yoder Smokers YS640s Pellet Grill to 250°F, set up for smoking.
Combine the beef stock and Cattleman’s Grill Butcher House Brine in a marinade shaker and mix well. Pour off 1/2 cup of the mixture and save for the wrap. Load the remaining liquid into your pistol grip injector and inject the brisket flat in a grid pattern.
Wipe excess liquid from the surface of the brisket. Season with Plowboys BBQ Bovine Bold.
Smoke the brisket flat on the second shelf of the grill until a dark red mahogany bark is formed on the surface, about 7-8 hours.
Remove from the grill and lay on top of two sheets of heavy duty foil. Add the 1/2 cup reserved injection liquid. Wrap the brisket tight with both sheets of foil.
Continue cooking until the brisket is probe tender, and the internal temperature passes 203°F. Remove from the smoked and let rest at least 1 hour before slicing. Slice thin for the sandwich.
While the brisket rests, make the onion rings. Fill a deep skillet with a few inches of vegetable oil. Bring oil temperature to 350°F-375°F.
Combine the flour and beer in a bowl. Add one tablespoon Plowboys BBQ Bovine Bold. Whisk to combine.
Combine the panko and remaining tablespoon Plowboys BBQ Bovine Bold in a separate bowl and mix to combine.
Dip the onion rings in the batter, then the panko, then transfer to the hot oil. Cook until golden brown on bottom, then flip and cook until the entire onion ring is golden brown. Transfer to a jerky rack over a sheet pan.
To build the Z-man Sandwich, spread the Kansas City Cowtown BBQ Sauce on the bottom bun of a toasted Kaiser roll. Top with thin sliced brisket and smoked provolone cheese (can be melted in grill/oven/broiler), then more bbq sauce and the top bun.