For the crepes:
In a medium bowl, lightly whisk the eggs. Then whisk in all of the remaining ingredients. Cover bowl and chill overnight (or 15-30min at room temp).
Set the batter out to come to room temperature for an hour before cooking. Preheat a large 10” skillet over medium-high heat. Add a small pat of butter and use a paper towel to quickly spread the butter around the pan. Add 1/4 cup of batter and tilt the pan so that the batter spreads into a circle. Cook each side for 1 – 2 minutes, or until golden brown. Unused crepes can easily be stored wrapped in the fridge for a couple of days, or frozen for several months.
For the filling:
Heat the oil in a pan without nonstick coating. Add onions, season with salt, and cook until softened. Add mushrooms. Cook until mushrooms have shrunk and begun to turn golden. De-glaze pan with the wine and add seasoning.
Makes 20 or so crepes. The recipe halves well.