There is a version of the Sandwich au Jambon de Bayonne that is less about the bread than about how thin the cured ham can be cut. Jambon de Bayonne is the dry-cured, salt-rubbed leg of the Pays Basque, often touched with the local red pepper, matured until it is deep red and dense. On a baguette it is not stacked but draped: ribbons laid almost translucent over the crumb, light enough that the bite parts cleanly instead of pulling the whole slice out.
That thinness is the entire technique. Cut thick, the ham turns leathery and its salt dominates everything around it; cut fine, it gives nuttiness and depth without weight. The butter underneath, spread thick and kept cool, is the counterweight the build needs, because a dry-cured leg brings concentration but no moisture and bare bread against it reads as harsh. The crust has to be firm enough to answer the firmness of the meat. This is a sandwich that survives a short wait, since there is little moisture to slacken the crumb, but it is still best within a few minutes of assembly, while the butter holds and the crust still bites.
It is the dry-cured reading of the canonical Jambon-Beurre: same baguette, same butter, a salt-cured southwestern leg in place of the pale poached ham, the knife doing most of the work.