To make the filling, melt 1 tablespoon butter in a large skillet over medium heat. Add mushrooms and salt and cook until mushrooms are browned, stirring frequently (about 10 minutes). Stir in herbs and transfer to a bowl.
Return skillet to medium heat and melt remaining tablespoon of butter. Stir in flour and cook for 1 minute, stirring continuously. Add cream and stir until thickened. Return mushrooms to skillet and stir in nutmeg.
To assemble the crêpes, spoon about 3 tablespoons of mushroom-herb filling onto the bottom third of each crêpe and roll it closed, rolling toward the uncovered portion. Place crêpes seam-side down in a buttered baking dish and bake at 425° until heated through, about 8–10 minutes.