Crepes are fun to make with a partner. The person in charge can make the crepes and let the helper work on the filling. When the crepes are ready to fill, both can pitch in. These feature oyster mushrooms, which are pale gray to dark brown and have a meatier texture than button mushrooms. Raw, they have a robust, slightly peppery flavor that mellows when cooked.
To prepare the crepes, lightly spoon 3/4 cup flour into dry measuring cups, and level with a knife. Combine flour and 1/8 teaspoon salt in a bowl. Add the milk, egg, and egg white, stirring with a whisk until almost smooth. Cover batter; chill 1 hour.
Place an 8-inch crepe pan or nonstick skillet coated with cooking spray 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 the edge of crepe with a spatula to test for doneness. The 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; cool. Repeat procedure with remaining batter. Stack crepes between single layers of wax paper or paper towels to prevent sticking.
Preheat oven to 350°.
To prepare the filling, melt butter in a large nonstick skillet over medium heat. Add the shallots, and saute for 3 minutes. Add the mushrooms, thyme, and garlic; saute 5 minutes. Sprinkle the mushroom mixture with 3 tablespoons flour; cook 1 minute. Gradually stir in broth, sherry, 1/4 teaspoon salt, and pepper. Bring mixture to a boil; reduce heat, and simmer until thick (about 2 minutes). Remove from heat, and reserve 1/2 cup mushroom mixture. Stir the chicken into remaining mushroom mixture.
Spoon about 1/3 cup chicken mixture onto center of each crepe. Bring 2 opposite sides to center; fold over filling. Place filled crepes, seam sides down, in a 13 x 9-inch baking dish coated with cooking spray. Spoon the remaining 1/2 cup mushroom mixture over crepes, and sprinkle with cheese. Bake at 350° for 15 minutes or until thoroughly heated.