After resting the crepe batter in the refrigerator overnight, the batter will look separated. Just whisk it up again until smooth. If there are lumps of flour or pieces of butter visible, blend the batter in your blender until smooth.
Heat a 6-inch non-stick skillet over medium heat until hot. Lightly brush the pan with 1/4 teaspoon butter. The pan should be hot enough that the butter and batter sizzles when it hits the pan, but not so hot that it turns the crepes brown and crispy.
Measure slightly less than 1/4 cup (about 3 tablespoons) of batter into the center of the pan, then swirl it around until the batter coats the bottom of the pan in a thin layer. Cook for about 1-2 minutes, until the edges of the crepe look "lacey", and the center of the crepe is set. Don't flip the crepe.
Use a silicone spatula to loosen the edges (if the crepe is done, it should very easily scoot around the pan), then very gently slide the crepe off the skillet onto a plate.
Grease the pan with another 1/4 teaspoon of butter, and cook the next crepe. Continue cooking crepes until you've cooked all the batter. As you stack the cooked crepes, you can keep them warm by over-turning a large bowl on top of the plate.