In Puebla, home of chiles en nogada, you can buy your walnuts already peeled. Good cooks say the dish is best made in August because that is when the new crop of walnuts is in. I saw that the nuts were "pecans" in the English menu at El Trapiche, but thought that it was an error in translation. Guess not! But now that I've tried the pecans, I like them too. The sauce is not as white as when made with peeled walnuts, of course.
Seeing how food sits "out" in Mexican homes makes me a bit nervous...we made the picadillo filling the night before. It was cooked in a cazuela (earthenware pot) on top of the stove, the ingredients added in a certain order, and it was considered important never to stir the dish, but to just push the mixture around a bit as each new ingredient was added. Then it just sat on the stove.
The peppers were roasted, then stuffed, battered and fried that morning. The walnut sauce was made just before serving. Serving chiles en nogada was a big event, one that called for the lace tablecloth and at least one grandmother in attendance!