Burger Sauce: In a small pot combine mayo, bbq sauce, dijon mustard, smoked paprika, onion powder, salt, sugar and cayenne pepper. Taste test for seasoning/spice and adjust accordingly.
Prep Fried Onions: Soak onions in a bowl of buttermilk (enough to cover the onions) for 30-60mins. If you're short on time just leave to soak as you prep the other steps. In a large shallow dish combine flour, paprika, baking powder, salt and white pepper. Use tongs to grab a small batch of the onions, give them a good shake to remove excess buttermilk, then add into the flour. Use a fork (or your hands) to fully coat them, shake off excess flour then place on a tray and repeat.
Cook Fried Onions: Heat up oil in a suitably sized pot to 180C/350F. Use a slotted spoon to lower in a batch of onions and use tongs to separate them as they hit the oil. Leave to fry for 2-5mins (depending on thickness) or until deep golden and visibly crispy. Remove and place on kitchen paper, bring oil temp back up to 180C/350F and repeat with the next batch. Sprinkle with salt as they rest to pull out the last bit of moisture.
Prep Patties: Very gently mould beef into 3 equal sized burger shapes (don't overwork the meat). Push down the centre of each burger to make a mini dome shape (will help with shrinkage). Heavily season both sides with salt and black pepper.
Cook Patties: Heat a drizzle of oil in a heavy base pan over high heat until smoking. Add patties and fry for a couple of minutes until they begin to crust/char on the bottom. Flip (don't press down), add cheese and fry for another couple of minutes until nicely charred on the other side. Remove and place to one side until needed.
Make Burgers: Stack in the following order - bottom bun, burger sauce, lettuce, tomato, bacon, patty, fried onions, top bun spread with more burger sauce. Serve up and enjoy!