This recipe comes from King Arthur. I made minor changes to reflect more generic ingredients. According to them, the best bread for thin-slicing is called pain de mie, a butter- and milk-rich loaf baked in a special lidded 13" x 4" x 4" pan. The lid ensures that the baking bread won't expand too much, keeping it very close-grained-and thus totally non-crumbly, and easy to slice. You can use all all-purpose flour without the whole wheat.