Pre-heat the oven to 300°. Coat the bottom of an oven-proof baking dish with cooking spray or melted butter.
First make the crepe mixture to give the batter time to rest. In a large bowl, whisk the flour, salt, eggs, melted butter, and chives until well mixed. Refrigerate batter for 30 minutes before making crepes.
To make the filling, add the butter to a large skillet over medium heat, sauté mushrooms until they start to become slightly golden, about 3-4 minutes. Add the leeks and sauté along with the mushrooms, about 2 to 3 minutes. Add the garlic and cook for 20 to 30 seconds. Season with salt, and pepper. Remove the veggies from the pan and set aside.
To make the bechamel sauce, use the same pan used to cook the mushroom mixture. Melt the butter over medium heat, add the flour, and cook, stirring constantly, for 1 minute. Season the roux with paprika, salt, pepper, and nutmeg, Whisk in the milk and Dijon mustard. Add the grated gruyere, and parmesan and stir to combine, simmer over medium-low heat until thick and creamy, about 3 minutes. Remove from the heat and set aside.
To cook the crepes, melt 3 to 4 tablespoons of butter in a small bowl. Heat crepe pan over medium heat. When the pan is hot brush with the melted butter, then pour about ¼ cup of batter in the center. Immediately use a tool or tilt the pan to spread out. Cook for 30-60 seconds or until the top loses its shine then flip using a crepe or offset spatula and cook for another 30 seconds. Brush with butter before each new crepe is poured.
To assemble the crepes, place 2 tablespoons of the chicken, and 2 tablespoons of the mushroom mixture down the center of one crepe. Add 2 tablespoons of the cheesy bechamel, and roll the crepe around the filling.
Carefully place in the prepared pan, putting the seam on the crepe on the bottom. Spoon ½ cup of sauce over the top of the crepes. Top with more cheese, if desired.
Cover the pan with foil and bake for 20 minutes.
Garnish crepes with chives and serve immediately. Enjoy!
