From America's Test Kitchen Season 2: French Toast, Waffles, and Breakfast Strata
You cannot simply put pancake batter in a waffle iron and make waffles; waffles should be moist and fluffy inside and crisp and brown outside—more like a soufflé with a crust than a pancake. We wanted to find the way to achieve this archetypal waffle.
Thick batter is the secret of the crisp exterior and custardy interior of a waffle, so we used a higher proportion of flour to liquid than that of standard recipes. With buttermilk (and buttermilk makes the best-tasting waffles) there’s no need for baking powder, and we found that eliminating it also helped crisp up the waffles. A small amount of cornmeal added a pleasing crunch. Separating the egg and folding the whipped white into the batter was a definite improvement; we could see the pockets of air when we cut into a waffle made this way. Like pancakes, waffles turn tough when the batter is overmixed, so we used a light hand, adding the liquid gradually and using more of a folding motion to mix. Cooked to a medium toasty brown, these waffles were everything we wanted them to be.
The secret to great waffles is a thick batter, so don’t expect to pour this one. Make toaster waffles out of leftover batter—undercook the waffles a bit, cool them on a wire rack, wrap them in plastic wrap and freeze. Pop them into the toaster for a quick breakfast.