Put all the crepe ingredients into a blender in the order listed and blend until the batter is smooth. Remove lid, scrape down the sides with a rubber spatula and briefly blend the mixture again. Set the covered blender in the refrigerator for at least 30 minutes but can be in refrigerator for up to 2 days.
When going to cook the crepes, use a paper towel to spread about a teaspoon of butter or vegetable oil in the bottom of an 8 or 9 inch nonstick skillet with low sides or a crepe pan. Heat the skillet on a stovetop burner, set at medium. Blend the batter again to smooth it.
For each crepe, pour one fourth to one third cup of batter into the skillet. Once you pour the batter into the pan, immediately tilt and move the pan to evenly coat the bottom. This should take about 5 seconds. Cook the crepe on the first side for about 45 seconds, then quickly flip it with a spatula and cook the other side for about half as long. Grasping the pan securely, quickly invert it so the cooked crepe will fall onto a large plate. Wipe the skillet with a paper towel and rub a little butter in the pan before cooking the next crepe.
Gently boil chicken in 4 quarts of water And 1 tablespoon of salt until cooked. When chicken is cool, cut into bite size pieces. Reserve 1 1/4 cups of the used water for broth.
Sauté mushrooms in butter until soft. Add flour, broth, cream, sherry, and white cheddar cheese, stirring well after each. Blend until smooth. Add 1 cup of cream sauce to chicken.
Place 3 tablespoons chicken mixture in each crepe, roll up and place in buttered casserole dish. Pour remaining sauce over crepes and sprinkle with Parmesan cheese. Bake at 375 degrees for 20 minutes.
Skipping the mandatory refrigeration period for crepe batter produces tough, rubbery pancakes because gluten strands fail to relax properly. Chilling the blended mixture for 30 minutes allows hydration of the flour proteins, yielding a delicate structure capable of holding heavy fillings without tearing.
Adapting Fillings and Starches
Swapping all-purpose flour for a gluten-free one-to-one baking blend works well in the batter, provided you add an extra egg white to compensate for lost elasticity. Dairy sensitivities require substituting full-fat canned coconut milk for heavy cream and using plant-based hard cheeses, though the sharp tang of white cheddar will be replaced by a milder profile. Keeping the cooking temperature at medium prevents the butter from scorching before the thin layer of batter sets.
Balancing Flavor and Texture
Dry cooking sherry introduces acidity and complex ethanol compounds that cut through the richness of heavy cream and melted white cheddar. Sautéing the sliced mushrooms until all moisture evaporates concentrates their umami compounds before flour is introduced to create the thickening roux. Baking the assembled crepes at 375 degrees Fahrenheit for 20 minutes ensures the Parmesan cheese on top melts into a golden crust without drying out the chicken interior.