01 - In a large bowl, whisk together flour, sugar, baking powder, baking soda, and salt. In another bowl, whisk together milk, eggs, melted butter, and vanilla extract. Mix wet into dry ingredients until just combined; do not overmix.
02 - Preheat waffle iron. Lightly grease, then cook waffles according to manufacturer's instructions until golden and crisp. You'll need 8 waffles (4 burgers, top and bottom). Set aside and keep warm.
03 - Preheat oven to 400°F. Arrange bacon on a foil-lined baking sheet. Bake for 12–15 minutes, then brush both sides with maple syrup. Return to oven for 3–4 minutes, until caramelized and crispy. Cool slightly, then halve slices.
04 - Form ground beef into 4 equal patties. Season with salt and pepper.
05 - Heat a skillet or grill over medium-high heat. Cook burgers 3–4 minutes per side for medium, topping each with a cheddar slice during the last minute to melt.
06 - Whisk together mayonnaise, maple syrup, Dijon, and a pinch of salt in a small bowl.
07 - Butter one side of each waffle and toast lightly in a skillet until golden.
08 - Spread maple aioli on one waffle. Top with arugula, burger patty, maple bacon, and red onion. Close with a second waffle. Repeat for all servings.
09 - Serve immediately while warm.