150g buckwheat flour (5.3 ounces; about 3/4 cup plus 3 tablespoons)
100g all-purpose flour (3.5 ounces; about 3/4 cup, spooned)
7g kosher salt (1/4 ounce; about 1 1/2 teaspoons)
1 large egg
300ml (1 1/4 cups) whole milk
325ml (1 1/3 cups) water
Unsalted butter, for cooking
Optional: fried eggs, grated Gruyère cheese, and thinly sliced ham, for filling
1 - In a large bowl, whisk together buckwheat flour, all-purpose flour, and salt. Add egg, milk, and water and whisk until thoroughly combined and slightly aerated. (Small bubbles should initially form on surface when batter is left to stand.)
2 - In a nonstick skillet or well-seasoned carbon steel crepe pan, melt about 1/2 tablespoon (7g) butter over high heat until browned and starting to smoke. Add just enough batter to thinly coat bottom of pan (about 80ml; 1/3 cup), swirling to evenly cover. Return to heat and let cook until bottom is beginning to brown well and top looks dry, 30 seconds to 1 minute. (To make sure, check the bottom for browning by gently lifting an edge of the crepe.) Reduce heat at any point to prevent burning.
3 - To Fill the Crepes: Start by spreading a small handful of grated Gruyère cheese around the center of the crepe while it's still in the pan, on the heat. Lay a slice of ham on top of cheese and slide a fried egg on top of ham. Using a thin metal spatula (being extra careful not to scratch pan if nonstick), fold sides of crepe in to form a rectangular shape with egg yolk exposed. Continue to cook until bottom is well browned and crisp, about 30 seconds. Serve, then repeat with remaining crepe batter, butter, and fillings.
4 - To Make Crepes for Another Purpose: Carefully free crepe from pan with a thin metal spatula (being careful not to scratch pan if nonstick), then flip and cook other side for about 10 seconds. Transfer to a plate. Continue with remaining crepe batter and butter. Keep cooked crepes stacked and covered with a clean kitchen towel while cooking remaining crepes. Crepes can be held for about 1 hour before using, then quickly reheated in a skillet.
Recipe from Serious Eats