Combine shredded cabbage and sliced jalapenos in a bowl. In a separate bowl mix milk, mayonnaise, vinegar, sugar, salt, and cayenne. Pour over cabbage. Toss to combine. Cover and refrigerate two hours.
Before serving, toss in cilantro leaves.
Heat canola oil in a heavy pot over medium high heat. Season chicken, then sear on all sides until skin is golden brown and some fat is rendered. Remove chicken from pot and pour off excess grease.
Add sliced onions and whole garlic cloves to pot and stir around to cook for 2 minutes. Pour in barbecue sauce, add chicken to the sauce, and place lid on the pot.
Place in a 300 degree oven for 1 1/2 hours, or until chicken is falling off the bone.
Remove the whole garlic cloves from the pot and set it aside. Remove chicken from pot and allow to cool enough to handle. Using hands or two forks, remove the meat from the bones. Finely shred the chicken using your hands or two forks.
Carefully skim off the excess fat that has risen on top of the sauce. Return shredded chicken to the pot and stir into the sauce. Reheat so that it's warm.
Spread butter on kaiser rolls and toast on the griddle.
To serve, place a good amount of chicken on the bottom half of the roll. Top with one or two garlic cloves, then a good helping of slaw. Top with the other half of the bun and dig in!