Crepe batter needs to stand before using!
Sift flour into a bowl. Add eggs, beat, but not vigorously. Add 3 Tbsp. milk, mix well. Whisk in remaining milk. (Remember, crepes are essentially pancakes, and suffer from overbeating.) Your batter will be fairly runny.
Melt butter, allow to cool. When cool, add to batter. Add salt.
Let batter stand one hour.
Brush a crepe pan
with oil. Heat pan, then add 2 Tbsp. of batter. Lift and turn the pan to distribute the batter evenly over the surface of the pan. Cook 3-4 minutes. The underside will be set and golden brown. You will be able to see the done-ness creep in from the outer edge to the middle. Carefully flip with a thin spatula or with your fingers (careful!) and cook the other side 2 minutes. Slide crepe onto a plate and repeat the process until the batter is gone.
Preheat oven to 350 degrees F. Spray a 9 x 13 rectangular baking dish with nonstick spray.
Wash the spinach, then cook for 5 minutes in just the water clinging to the leaves. Drain, squeeze out as much liquid as possible. Chop spinach.
Melt 2 Tbsp. butter in skillet. Add spinach, cook over low heat, 5 minutes. Stir frequently. Remove spinach to mixing bowl. Add ricotta and egg yolk.
Spread mixture on crepes and either roll or fold in half and set in prepared baking dish. Sprinkle with Parmesan cheese, dot with 1 Tbsp. butter.
Bake 15 minutes at 350 degrees F. Let stand a few minutes before serving.
Adapted from The Silver Spoon