This looks funny, is child’s play for anyone to make, and just as long in advance.
Spread a thin layer of butter on the salami slices and stack them on top of each other with precision. The top slice remains empty. The stack should be about 8 to 10 inches high (about as high as a slice of the whole wheat bread is wide). Wrap in aluminum foil and refrigerate overnight to firm up.
To serve, slice the stack on the slicer diagonally to salamiduenn slices. Bed these striped slices on whole wheat bread and cut into bite-sized bites. Arrange them end to end on a platter for serving.