| 2/3 cup buckwheat flour | 2 large eggs | |
| 1/3 cup unbleached all-purpose flour | 1 tablespoon mayonnaise | |
| 1 tablespoon sugar | 1/2 teaspoon Dijon mustard | |
| 1/4 teaspoon kosher salt | 1/2 pound sliced Swiss cheese | |
| 4 tablespoons unsalted butter, melted and cooled slightly, plus extra for cooking | 1 pound sliced ham | |
| 2 cups milk |
In a large bowl, whisk both flours, sugar and salt together.
In a small bowl, whisk the butter, milk and eggs together, then whisk into the dry ingredients until well combined. The batter will be thin.
Refrigerate for at least an hour to let the liquid fully hydrate the flour. (The batter can be refrigerated overnight for morning crêpes; let it sit it on the counter for at least 15 minutes in the morning to warm up slightly before cooking.)
Stir the mayonnaise and mustard together.
Melt a dab of butter in a crêpe pan or nonstick skillet over medium heat.
Add 1/2 cup batter to the pan, swirling to cover thinly but evenly. Cook until the edges of the crepe turn golden brown, then loosen with a spatula and flip.
Layer two slices of cheese, a thin swipe of the Dijon mayo, and two slices of ham down the center of the crêpe, and cook until the cheese melts.
Roll the crêpe into thirds to make a loose cylinder, then remove from the pan and serve.