Refresh spinach in a large bowl of ice water by tossing into cold water, swishing around and placing in colander. It will take a couple of batches to do this. Don’t try to drain all the water, it will be helpful in steaming the greens. Place all the spinach in a big pot and turn to high. Add lid and time for two minutes. Spinach will be mostly steamed. Use a slotted spoon to turn over any unwilted leaves to the bottom, replace lid, and steam for one more minute. Drain well in colander. Set aside. Squeeze out any excess water before adding to the cheese sauce.
Mix all ingredients together until smooth; batter will be very thin. A blender is ideal for this recipe.
Preheat crepe pan or round 9 or 10" pan on low to medium-low heat. Generously pre-grease pan before making every crepe. Pour ¼ cup of batter into skillet and quickly rotate pan in circular motion to disperse the batter into a thin, even coat. Air holes will appear, do not try to fill them. When edges start to brown, lift edges of crepe with spatula, then flip. Remove crepe and place flat on parchment or wax paper. Use a paper liner in between crepes when stacking while continuing to cook additional crepes. Keep crepes covered to prevent drying out.
In a medium sauce pan, melt butter over low heat, add the flour and seasonings, and stir constantly with a wire whisk for a couple of minutes, until thickened. Slowly add the milk, whisking constantly to prevent lumps. Cook over medium/low heat until very rich and creamy. Adjust temperature to low and add the grated cheese, small amounts at a time, stirring to smooth between additions.
Squeeze the excess moisture out of the spinach, add to the warm cheese sauce, and stir to distribute evenly.
Lay out one crepe, pretty side down. Spread a generous amount of filling down the middle of the crepe. Fold one side in over the filling, and then fold the other side over again. Serve immediately while warm or assemble all the crepes in a sprayed baking dish. Cover with foil, and re-warm in a preheated 325°oven for about 30 minutes, until filling is just starting to bubble. Allow to stand for a few minutes if taking out of the oven.
Adapted from Joy of Cooking’s Cheese Sauce recipe.