Place flour in a medium bowl. Combine milk, 1 tablespoon margarine, and egg; add to flour, stirring with a whisk until almost smooth. Cover; chill 1 hour.
Coat an 8-inch crepe pan or nonstick skillet with cooking spray; place over medium-high heat until hot. Remove pan from heat. Pour a scant 1/4 cup batter into pan; quickly tilt pan in all directions so batter covers pan with a thin film. Cook about 1 minute.
Carefully lift edge of crepe with a spatula to test for doneness (crepe is ready to turn when it can be shaken loose from the pan and the underside is lightly browned). Turn crepe over; cook 30 seconds on other side.
Place crepe on a towel; allow to cool. Repeat procedure until all of the batter is used. Stack crepes between single layers of wax paper or paper towels to prevent sticking.
Preheat the oven to 350°. Prepare Bechamel Sauce; keep warm.
Melt 2 teaspoons margarine over medium-high heat in a large nonstick skillet. Add mushrooms, shallots, sherry, and garlic; saute 5 minutes.
Add parsley and chives to Bechamel Sauce; stir well. Add 1 cup bechamel mixture to mushroom mixture; stir well.
Spoon 1/4 cup mushroom mixture onto center of each crepe. Bring 2 opposite sides to center; fold over filling. Beginning at 1 short side, roll up crepe tightly, jelly-roll fashion. Place stuffedcrepes, seam sides down, in a 13 x 9-inch baking dish coated with cooking spray. Pour remaining bechamel mixture over crepes. Bake at 350° for 20 minutes.