Melt 5 tablespoons butter in an 8-inch nonstick skillet. Combine the melted butter, both flours, the milk, eggs and salt in a blender and process until smooth (set the skillet aside). Let the batter rest at room temperature at least 1 hour or overnight. Stir in the parsley, if desired.
Preheat the oven to 300 degrees. Heat the skillet over medium heat until a drop of water sizzles in it. Lightly butter the skillet, then add a scant 1/3 cup batter and quickly swirl to coat the bottom of the pan. Cook until the crepe sets and browns around the edges, about 2 minutes. Carefully lift with a rubber spatula, flip over and cook about 30 more seconds. Transfer to a plate.
Repeat with the remaining batter, adding more butter as needed and stacking the finished crepes. Wrap the crepes in a damp dish towel and place in the oven to reheat, about 10 minutes.
Serve with assorted fillings.
Sweet Onion Crepe Filling:
Heat 2 tablespoons butter in a large skillet over medium-low heat. Add 2 sliced onions and 2 thyme sprigs. Season with salt and pepper and cook until the onions are lightly browned, about 20 minutes.
Sauteed Spinach Crepe Filling:
Heat 2 tablespoons olive oil in a large skillet over medium-high heat. Add 12 ounces spinach and cook until just wilted, about 4 minutes. Season with salt and pepper.
Creamy Mushroom Crepe Filling:
Heat 3 tablespoons butter in a large skillet over medium-high heat. Add 1 pound chopped wild mushrooms and 2 thyme sprigs; saute until the mushrooms are golden, about 10 minutes. Season with salt and pepper and add 2/3 cup heavy cream; toss to warm through. Remove from the heat and add a handful of parsley.
Citrus Shrimp Crepe Filling:
Yield:Photograph by Con Poulos
Saute 1 1/4 pounds shrimp (peeled and halved lengthwise) in 2 tablespoons butter with 1 strip lemon zest, 2 tarragon sprigs and salt and pepper until the shrimp turn pink, 3 to 4 minutes. Add a squeeze of lemon juice and 1/2 cup white wine and simmer 1 minute. Remove from the heat; add 4 tablespoons chopped cold butter and some parsley.
You can make the crepes a day ahead. Just wrap in plastic and refrigerate, then reheat before assembling.