The crepes can be refrigerated, wrapped in plastic wrap, up to two days; or frozen, wrapped in paper towels (to absorb moisture when thawing) and plastic wrap, and placed in a freezer bag, up to one month. Thaw completely before filling. The mushroom filling can be made two days ahead and stored in the refrigerator. When Martha made these crepes on Cooking School episode 404, she made a half recipe and finished each serving with a fried egg.
These mushroom cups can be frozen for up to one month and popped directly into the oven from the freezer (add two minutes to the cooking time). If you put them in while the meat is resting, they'll be ready just in time for dinner.
The secret to mushrooms that are beautifully browned and not watery is taking a hands-off approach. Stirring them as they caramelize releases the mushrooms' liquid and causes them to steam, so leaving them alone is the way to go.