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—do not overmix.
02 - Preheat waffle iron and lightly grease with cooking spray or oil. Cook waffles according to manufacturer's instructions until golden and crisp. You'll need 8 waffles total (4 tops and 4 bottoms). Keep warm until ready to assemble.
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 and halve each slice.
04 - Divide ground beef into 4 equal portions and gently form into patties slightly larger than the waffles. Season both sides generously with salt and pepper.
05 - Heat a skillet or grill over medium-high heat. Cook burgers for 3–4 minutes per side for medium doneness. Place a cheddar slice on each patty during the last minute of cooking and cover to melt.
06 - Whisk together mayonnaise, maple syrup, Dijon mustard, and a pinch of salt in a small bowl until smooth and well combined.
07 - Butter one side of each waffle. Place buttered side down in a skillet over medium heat and toast lightly until golden and crispy, about 1–2 minutes.
08 - Spread maple aioli on the toasted side of a waffle. Layer with arugula, burger patty with melted cheese, maple bacon halves, and red onion slices. Top with a second waffle. Repeat for remaining servings.
09 - Serve immediately while warm and crispy. Consider securing with sandwich picks if needed.