Unleash Your Inner Chef with this Perfect BBQ Burger!

Combine onions and buttermilk in a bowl and soak at room temperature for 1 hour.

Pour oil to a depth of 1 1/2 inches into a deep, heavy-bottomed skillet or pot or a deep-fat fryer; heat to 350 degrees F (175 degrees C).

Meanwhile whisk together flour, 1/4 teaspoon salt, black pepper, cayenne, and 1/4 teaspoon paprika in a large bowl for the breading. Remove onions from buttermilk, allowing excess to drip off. Toss onions in the breading until well coated.

Set a wire rack on a rimmed baking sheet. Working in 3 batches, fry onions, turning occasionally to break up any clumps, until crisp and golden, 1 to 2 minutes. Transfer to wire rack to drain. Repeat with remaining onions.

For rub, stir together 1/2 teaspoon smoked paprika, celery salt, chili powder, garlic powder, onion powder, and remaining 1/2 teaspoon salt in a small bowl. Shape beef into 4 patties, about 4 inches in diameter. Brush patties with oil; sprinkle both sides with rub.

Preheat grill to medium-high and lightly oil grate. Grill patties, uncovered, about 5 minutes or until slightly charred.

Flip patties; brush barbecue sauce evenly over patties. Continue cooking about 3 minutes more or until charred and a thermometer inserted into centers registers 160 degrees F (70 degrees C). Top patties with cheese; grill, covered, until cheese is melted, about 1 minute more. Grill buns, cut sides down, uncovered, until toasted, 30 seconds to 1 minute.

Spread buns with mayonnaise and additional barbecue sauce. Fill buns with patties, onion straws, tomato, and lettuce. Serve immediately.