Divide the meat into 6 balls and pat into smaller slider size patties. Add the buttermilk to a shallow bowl. To another shallow bowl, add the cornflakes, Panko, flour and cajun seasoning.
Working in an assembly line, dip the patties, one at a time through the buttermilk and then dredge through the cornflakes, coating the patties completely. Place breaded patties on a plate and repeat with the remaining patties.
Heat a large skillet over medium high heat and add a drizzle of olive oil. Once the oil is sizzling, add the burgers and cook until golden brown and cooked through, about 3-4 minutes per side. During the last few minutes of cooking, add the cheddar cheese to each burger.
To serve, place a burger on a warmed bun and drizzle with the black pepper rub sauce (recipe below). Top with onion rings and serve with ranch.