Sift together flours and sugar (if using), then beat in eggs, milk, melted butter, salt and vanilla (if using) until batter is smooth.
Let batter rest in refrigerator overnight, or at least 30 minutes.
When ready to cook, heat a crepe pan or flat frying pan over medium. Lightly coat with nonstick spray or add a small amount of butter to melt.
When pan is hot, pour about 1/4 cup of batter into the center of the pan. Tilt pan to evenly coat it with batter, or use a rateau to spread.
Cook crepe until edges are crispy and the top no longer looks wet (about 2 minutes). Flip and cook for another minute or so. Fold crepe and set aside until the whole batch is done.
Repeat with remaining batter. Serve crepes with your choice of toppings, such as ham and cheese, fresh fruit, or Nutella.
Notes
Batter should rest for at least 30 minutes, but is even better if you give it overnight.
If celiac, be sure to check the buckwheat flour packaging to ensure it is produced in a gluten-free facility.