Riad Nasr and Lee Hanson, cochefs of the star-studded Manhattan eatery Balthazar, share their recipe for buckwheat crepes.
Whisk together flours and 1/2 teaspoon salt into a medium bowl. Whisk in 2 eggs, 1 1/2 cups milk, and 2 tablespoons melted butter; whisk until smooth. Cover bowl with plastic wrap and refrigerate at least 30 minutes and up to overnight.
Preheat oven to 200 degrees. Remove batter from refrigerator and whisk in remaining 1/4 cup milk.
Place an 8-inch nonstick skillet or crepe pan over medium heat. Add 1/2 teaspoon melted butter and use a crumpled-up paper towel to spread evenly. Add a scant 1/4 cup batter and quickly swirl to coat the bottom of the pan.
Cook until edges begin to dry, about 1 minute. Using your fingers or tongs, turn crepe, continue cooking about 15 seconds more; transfer to a plate and keep warm in the oven. Repeat process with remaining melted butter and batter, stacking each crepe on top of one another as you work.
Using a fork or a whisk, blend remaining 12 eggs, remaining 1/2 teaspoon salt, and 2 tablespoons water in a large bowl. Melt remaining 4 tablespoons butter in a large nonstick skillet over medium-low heat. Add eggs and begin stirring with a wooden spoon. Slowly drag the spoon around the bottom and sides of the pan until thickened, about 5 minutes. Continue stirring until eggs have formed loose, moist curds, 3 to 5 minutes more. Remove from heat; set aside.
Increase oven temperature to 400 degrees.
Butter a 9-by-13-inch baking dish; set aside. Place a crepe, dark side down, on work surface. Layer a slice of ham, some of the Gruyere, and about 1/4 cup eggs on top of crepe. Roll crepe and place seam side down in baking dish. Repeat process with remaining crepes. Transfer baking dish to oven and bake for 5 minutes. Serve immediately.