Oh, those French bakers. They take great pains (no pun intended) to make slender baguettes with thick, shatteringly crisp crusts. And yet, as if to thumb their noses at the whole artisan baking thing, they also crank out rectangular sandwich loaves with virtually no crusts at all. Pain de mie (“bread of crumb”) is the anti-baguette. A baguette takes days to make and goes stale after three hours. Pain de mie takes about three hours to make and stays fresh for days. (Julia Child said it tastes even better after a day or two.) Enriched with milk, pain de mie delights with a fine, light crumb and holds its shape even when sliced thin…