In a large mixing bowl, whisk together the buckwheat flour, water, and salt. Cover and let sit for at least 30 minutes at room temperature. You can also prepare the batter the day before and let it rest overnight in the refrigerator.*
In the meantime, prepare the mushroom filling.
Mushroom Filling
Heat the oil in a non-stick pan over medium heat. Once hot, add the minced shallot and garlic, and sauté for about 2 minutes.
Next, add the sliced mushrooms and cook for another 3-5 minutes. Add the soy sauce and cook for one more minute.
Deglaze the pan with the white wine and cook for 5 more minutes, or until the liquid has reduced by about half. Next, stir in the nutritional yeast, rosemary, ground black pepper, and hummus. Stir to dilute the hummus. Remove from heat and cover to keep warm.
Assembling
Heat a non-stick skillet over medium heat. Once hot, add about one tablespoon of oil and use a kitchen paper towel to spread it evenly.
Make sure the batter has the right consistency, it should be pourable and quite thin. Pour 1/3 to 1/2 cup of the batter (depending on the size of your skillet) and tilt the skillet to spread the batter evenly and as thin as possible.
Cook over medium-high heat for 2-3 minutes, or until golden brown. Place about 1/3 of the mushroom filling in the center of the crêpe and cook for another 2-3 minutes, or until the crêpe gets crispy edges. Note: you can add a teaspoon of butter to the skillet and spread it around the crêpe to get crispier edges.
Finally, fold the edges of the crêpe over the filling to make a square pocket. Transfer the crêpe to a plate and serve immediately. Repeat with the remaining crêpes and filling.
Notes
* If making the batter the day before, you will have to add a little bit more water the next day in order to get a thin batter, as it will have thickened.