01 - Whisk together flour, sugar, baking powder, baking soda, and salt in a large bowl. In a separate bowl, combine milk, eggs, melted butter, and vanilla extract. Pour wet ingredients into dry ingredients and mix until just combined. Avoid overmixing to ensure tender waffles.
02 - Preheat waffle iron and lightly grease with cooking spray or oil. Cook waffles according to manufacturer instructions until golden brown and crisp. You will need 8 waffles total (4 burgers with top and bottom). Keep cooked waffles warm in a low temperature oven until assembly.
03 - Preheat oven to 400°F. Arrange bacon slices on a foil-lined baking sheet. Bake for 12 to 15 minutes until partially cooked, then remove from oven and brush both sides generously with maple syrup. Return to oven for an additional 3 to 4 minutes until caramelized and crispy. Let cool slightly, then cut each slice in half.
04 - Divide ground beef into 4 equal portions and gently shape into patties slightly larger than the waffles (they will shrink during cooking). Season both sides generously with salt and pepper.
05 - Heat a skillet or grill pan over medium-high heat. Cook burger patties for 3 to 4 minutes per side for medium doneness, or longer if preferred. During the final minute of cooking, place a slice of sharp cheddar cheese on each patty and cover briefly to melt.
06 - Combine mayonnaise, maple syrup, Dijon mustard, and a pinch of salt in a small bowl. Whisk thoroughly until smooth and well incorporated. Adjust seasoning to taste.
07 - Butter one side of each waffle. Place them buttered side down in a clean skillet over medium heat and toast until golden brown and slightly crisp, about 1 to 2 minutes per side.
08 - Spread maple aioli on one toasted waffle. Layer with baby arugula, cheese-topped burger patty, maple bacon halves, and red onion slices. Top with a second waddle and press gently. Repeat for remaining 3 burgers. Serve immediately while warm.