Add all ingredeints to a blender, and blend until smooth.
Heat your cast-iron skillet over medium heat. Using a basting/marinade brush lightly apply butter.
Pour appoximately ½ cup of batter onto the pan, swirling the pan to evenly coat.
When the top of the batter is dry and the edges start to curl up and brown, then you're likely ready to flip. I usually use a silicon spatula to lift the crepe, and a larger turner to flip the crepe.
Cook for another couple of minutes until the other side is golden brown. Remove from pan, set aside.
Repeat with the rest of the batter, lightly buttering the pan in between each crepe.
Notes
If necessary, you can substitute the buttermilk for milk.