In a bowl whisk together egg, milk, butter, and parsley until combined well. Add flour, salt and pepper and whisk until smooth. Set aside to rest for 30-60 minutes.
Heat a 6- to 8-inch nonstick omelet pan over moderately high heat until hot. Brush with oil and heat until hot but not smoking. Pour about 2 tablespoons of batter into the pan, tilting and rotating pan quickly to cover bottom with a thin layer. Cook until lightly brown then flip the crepe and cook until light brown on the other side.
Transfer crêpe to a plate. Continue with the remaining batter, brushing the pan with oil as needed.
To make the filling, heat 2 tablespoons of butter in a large sauté pan over medium high heat. Add the shallots and mushrooms and cook until the mushrooms release their liquid and the liquid evaporates, about 5 minutes. Add the sausage and cook 2 minutes. Remove from the heat and set aside.
Preheat oven to 200°
In a medium saucepan melt the remaining 2 tablespoons butter over medium high heat and whisk in flour. Cook stirring for 2 minutes. While continuing to whisk, add the milk in a slow steady stream. Cook, stirring constantly until thick, about 5 minutes. Add mushrooms, cream, parsley, bacon, salt and pepper to taste and simmer 10 minutes, or until very thick. Cool filling slightly.
Fill each crepe with ¼ cup of filling and roll or fold to close. Transfer to a buttered baking dish and bake until heated through, about 10 minutes.
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