Buttermilk brings slight tang and moisture to the batter, while olive oil offers fruity richness. Choose a mild-flavored (not too peppery) type of oil for these waffles.
INGREDIENTS (6 SERVINGS)
- 2 cups all-purpose flour
- ½ cup unsweetened cocoa powder
- ¼ cup (packed) brown sugar
- 2 teaspoons baking powder
- 1 teaspoon baking soda
- 1 teaspoon kosher salt
- 3 large eggs, separated
- 2 cups buttermilk
- ½ cup olive oil
- 1 teaspoon vanilla extract
- 6 oz. bittersweet chocolate (at least 70% cacao), finely chopped
- Nonstick vegetable oil spray
- Unsalted butter and warm pure maple syrup (for serving)
Preheat oven to 250°. Whisk flour, cocoa powder, brown sugar, baking powder, baking soda, and salt in a large bowl. Make a well in the center and add egg yolks, buttermilk, oil, and vanilla. Blend with a fork, then gradually incorporate dry ingredients, mixing just until combined.
Using an electric mixer on medium-high speed, beat egg whites in a small bowl until soft peaks form. Working in 2 batches, fold egg whites into batter just until combined. Fold in chocolate.
Heat a waffle iron until very hot; lightly coat with nonstick spray. Working in batches, cook waffles until cooked through. Transfer to a wire rack set inside a baking sheet, cover loosely with foil, and keep warm in oven until ready to serve.
Serve waffles with butter and syrup.
DO AHEAD: Batter with egg whites can be made 4 hours ahead. Cover and chill.