Peel the potatoes and cut into 1/4" width pieces. Slice the onion into 1/4" thick, and cut the ham into 1/4" strips.
Make the Dashi broth according to the recipe (or use instant dashi powder) and bring to a boil. Add potato, onion, and ham, and simmer for 10 minutes covered.
Remove from the heat and dissolve the miso paste.