Rectangular loaves of brioche bread are sold at many specialty bakeries and natural food superstores. Challah is similar to brioche, but it is usually braided and makes irregularly shaped slices. Although egg-enriched bread is my personal favorite, any good- tasting sandwich bread will do for this recipe. The proportions of the filling may change slightly with the size of the bread slices, so be flexible with the amounts. If your bechamel is too thick, whisk in additional heavy cream to reach your desired consistency.