Heat oven to 350. Melt 3 tbsp butter in microwaveable bowl. Add 3 eggs and milk, whisk. Add flour, 2 tbsp sugar, mix well.
Spray an 8" skillet w/ cooking spray. Place over med-high heat. Add 1/4 cup crepe batter to pan, tilt to cover whole pan. Cook until light brown, flip over and cook 20 seconds more. Transfer to a plate, repeat w/ remaining batter.
In lg skillet, melt remaining butter, cook mushrooms until tender. Add any remaining butter and egg whites. Cok until eggs are set, stirring often to scramble. Top each crepe w/ cheese, mushrooms, egg and scallions. Fold in 1/2., place in lg baking pan, Bake 5-10 mins or until cheese is melted.