Step 1: Set up your grill for indirect grilling and preheat to medium. This works best in a charcoal grill.
Step 2: Arrange the bratwursts on the grate over the drip pan. Toss the wood chips on the coals, half on each mound of coals. Cover the grill and adjust the vent holes to obtain a temperature of about 350 degrees. Smoke-roast the sausages until golden brown and cooked through, 30 to 40 minutes.
Step 3: Meanwhile, combine the beer, butter and grilled onion slices in a large grill-proof pan large enough to accommodate all the brats (I like to use a large aluminum drip pan.) When the brats are cooked through, transfer them to the beer bath, then put it on the grill.
Step 4: Keep the brats warm in the beer bath as long as you like, replenishing the fire with a couple extract coals on each side if needed to keep it smoldering.
Step 5: Serve the brats as they would in Wisconsin, on hard rolls with yellow ballpark-style mustard, or do them up BBQ U-style, with brown mustard, grilled onions and peppers and sauerkraut on a cut-up baguette.
Even if you’re a diehard gas griller, I recommend investing in an inexpensive, charcoal-burning kettle grill. It’s very difficult to get great smoke flavor from a gas grill.