Combine the milk and vinegar in a large bowl: the mixture will curdle and become like butter milk.
Stir in the oil, sugar, maple extract, and salt.
Add the flour, baking powder, and baking soda and stir until smooth, being careful not to overmix.
Cook the waffles according to the waffle iron instructions using nonstick cooking spray. You should get 2 Belgian-size waffles or 4 standard-size waffles. (For extra crispness, toast the waffles in a toaster oven before assembling and eating.)
To serve, break the waffles into quarters.
Add 2 tablespoons to ¼ cup of filling on top of one quarter, then top with another quarter.
Serve warm.