In a medium bowl, stir together the soy milk and vinegar. Let sit for 5 minutes to curdle and slightly thicken.
Preheat your waffle iron according to the manufacturer's instructions.
In a large bowl, whisk the flour, baking powder, sugar, and salt to combine well.
To the medium bowl with the buttermilk, add the oil, applesauce, and vanilla then whisk to combine well.
Add the wet ingredients to the bowl of dry ingredients and whisk until just combined. Don’t overmix. The batter will be thick and small lumps are fine.
If your waffle iron is not non-stick, lightly spray it with nonstick cooking spray otherwise leave it bare.
Spoon the amount of batter recommended by the manufacturer onto the hot waffle iron (typically, ¼-1/3 cup per waffle). Cook according to the manufacturer’s instructions until the waffle is golden brown. Let the steam dissipate before opening the waffle maker.
Serve immediately or set them on a cooling rack to allow air to circulate and reduce moisture buildup. To keep waffles warm, place them on an oven-safe cooling/baking rack in a 200°F preheated oven as soon as they come out of the waffle maker. Do not stack or overlap them.