Cut each rack of ribs in half. In a small bowl, whisk together paprika, garlic powder, mustard powder, ginger, salt, allspice and cayenne pepper. Rub spice mixture on both sides of each rack of ribs.
Place ribs on a large slow cooker, with wide ends down and meaty sides facing the wall. Cover and cook on low for 6 to 8 hours, until the ribs are fall off the bone tender.
Meanwhile, combine together the honey, soy sauce, ketchup, garlic and crushed red pepper flakes in a saucepan. Bring to a boil over medium high heat. Reduce heat to a simmer and cook for 15 minutes or until the sauce has thickened.
Preheat the broiler on high. Line a large, rimmed baking sheet with aluminum foil.
Carefully transfer ribs to the prepared baking sheet, meaty-side down. Brush sauce over the ribs and broil for 4 minutes. Carefully turn the ribs over, generously brush them with more sauce and continue to broil for another 4 minutes, or until the ribs are browned.
Remove ribs from the heat and tent with foil. Let rest for 10 minutes before serving.
Sprinkle top with sesame seeds and serve with leftover sauce on the side.