Slightly adapted from this recipe from Scarborough Fair Bed and Breakfast. Makes 6-8 waffles (serving size: 1-2 waffles per person).
1-1/2 cups cooked sweet potato (2 medium-large potatoes)
2 tsp minced rosemary leaves
2 cups all-purpose unbleached flour
1/4 tsp kosher salt
1 Tbsp baking powder
1/2 tsp black pepper
3 eggs, yolks and white separated
1-1/2 cups nonfat (skim) milk
1/3 packed light brown sugar
4 Tbsp unsalted butter, melted
1/2 cup finely grated Parmigiano-Reggiano cheese
Preheat waffle maker to 400°F.
Prick the sweet potatoes with a fork once or twice, and microwave for 9 minutes or until the potato is quite squishy. Let cool slightly, and scoop out the flesh. Mash well with a spoon, and set aside. (If you have leftover mashed potatoes, use 1-1/2 cups.)
In a large bowl, whisk together the rosemary, flour, salt, baking powder and black pepper.
In a separate bowl, whisk together the egg yolks, sweet potatoes, milk, brown sugar and melted butter, until the mixture is smooth. Stir in the cheese.
In a small bowl, whisk the egg whites until stiff peaks form (or use a hand mixer). The egg whites should be glistening, and should hold their shape.
Take 1/4 cup of the batter, and with a rubber spatula fold it into the egg whites. Then, fold all of the egg white mixture into the batter, taking care not to deflate the batter.
Pour half of the mixture on the bottom plate of the waffle maker, and spread evenly. Close the top, and cook for 5-6 minutes, or until the waffles are as crisp as you like them. Repeat with remaining batter.
Serve with a pat of butter on top.