Prepare the Buckwheat Crepes and set aside.
Peel the onions, cut them in half lengthwise, and then slice them thickly.
Heat a tablespoon of olive oil and a tablespoon of butter in each of two large non-stick pans, and divide the onions between them. Sprinkle about ½ teaspoon of salt over each batch and cook the onions on medium heat, stirring occasionally, until they are golden brown. This will take about 45 minutes. Add black pepper to taste.
Meanwhile, peel the apples, cut into wedges, and slice the wedges crosswise. When the onions are lightly browned and much reduced in volume, consolidate them into one pan. Add the Calvados to the onions and stir quickly to deglaze the pan. Add the sliced apples, and a touch more salt if needed. Continue cooking, stirring often, until the liquid is entirely gone, the onions are a deep caramel color, and the apples are tender.
Spoon 2 to 3 rounded tablespoons of the onion mixture across the center of a crepe, then sprinkle about ½ ounce of grated cheese over it. Roll the crepe loosely over the folling and place it seam side down on a buttered baking sheet. Continue filling and rolling crepes until all the onions and cheese are used up. You should have at least 16-18 filled crepes. Reserve any leftover crepes for another use.
Cover the crepes loosely with a piece of aluminum foil, and bake them in a 350 degree oven for 10-15 minutes, or until they are hot through and the cheese is completely melted. If you have filled the crepes earlier and kept them in the refrigerator for a while, adjust the oven time upward by at least 5 minutes.
Serve the crepes at once, with a green salad, and Cranberry-Jalapeno Sauce.