In a medium bowl, combine the milk and lemon juice. Allow to sit while you work on the batter.
In a medium bowl, whisk the flour, cornstarch, baking powder, and salt together; set aside.
In a separate bowl, using an electric beater on high speed, whip the egg whites until soft peaks form. Add the sugar, then continue whipping until stiff peaks form.
Add the egg yolks, oil, and extracts to the milk mixture and stir until well combined. Pour wet ingredients into the flour mixture and stir until just combined--batter should be lumpy. Gently fold in the whipped egg whites.
Cook batter in a waffle iron according to manufacturers instructions. Once cooked, serve immediately with lemon curd and meringue topping. Toast the topping with a kitchen torch, if desired.
If not serving right away, place waffles directly onto the (clean) rack of an oven that's been preheated to 200ºF, while you cook up and coat the rest of the waffles