Crepes

1. Combine crepe ingredients (except butter and oil), plus 1/2 teaspoon salt and a pinch of pepper, in the blender and blend at increasing speed until smooth. With blender running on low, drizzle in the melted butter, then empty into a bowl or liquid measuring cup. Heat a 6 to 8 inch nonstick skillet at just hotter than medium heat for about 5 minutes.
2. To make each crepe, brush pan with a small amount of oil. Hold pan in one hand and scoop 1/4 cup batter (for a 7″ pan) into a measuring cup in the other. Tilt the pan so the side farthest from you is angled up, pour the batter near the highest point of the pan, and swirl/tilt the pan to coat it with the batter.
3. Cook undisturbed about 45 seconds, until golden brown and visible side is nearly dry. Use a metal spatula (an offset spatula if you have one) to gently flip crepe over, cooking about 20 seconds on the other side, until very light golden in just a few places. With an upside-down “U” motion, lift pan then invert crepe onto a paper towel lined plate (don’t just rotate the pan from the handle, or the crepe may wrinkle or tear). Repeat process to make remaining crepes (about 10), letting pan heat around 15 seconds between crepes.
4. Stack the crepes as they’re finished. If not serving immediately, cool the stack, wrap in plastic wrap, and refrigerate up to a couple days.

Filling and sauce

1. In a 2 to 3 quart skillet or Dutch oven, heat 1 tablespoon each butter and oil over medium high until butter is melted and foaming. Add mushrooms and cook until tender, browned, and no liquid remains in pan (here’s the full tutorial to sauté mushrooms). Turn off heat and set aside in a mixing bowl. Heat another tablespoon each butter and oil in the same skillet over medium high. Add asparagus and cook until seared and tender, but not mushy, then add to the mushrooms. Season the veg mix to taste.
2. In a small saucepan, scald (heat gradually until small bubbles form at the edge of the pan) the milk, stock, and garlic. Turn off heat, cover, and reserve. In a medium saucepan or the skillet from the vegetables, melt 2 tablespoons butter over medium. Add onion and cook gently until tender but not caramelized. Sprinkle flour over the onions, reduce heat slightly, and stir constantly for 3 minutes.
3. Remove garlic from reserved liquid and discard, pour liquid into the onion pan while whisking, then raise heat to bring to a gentle simmer. Cook, stirring almost constantly, for 7 to 10 minutes, until thickened. Stir in mustard, lemon zest, truffle oil, fresh herbs, and plenty of salt and pepper to taste. Keep warm until serving.
4. To serve, warm crepes. Spoon a scoop of sauce into the middle of each crepe and top with a scoop of mushrooms and asparagus. Roll loosely then serve two to a plate, or place seam side down in an ungreased baking dish and keep warm in a low oven. Garnish with extra sauce, herbs, asparagus ribbons, and lemon zest.