Prepare Vinaigrette and set aside.
Steam each variety of potato separately:
To steam the potatoes, arrange whole potatoes on a steamer rack. Steam over 1 to 2 inches of boiling water, approximately 30 to 35 minutes. Check for doneness by inserting a sharp knife into the potato - there should not be any resistance. Remove from heat and let potatoes cool slightly, but still warm; cut into large chunks.
Place the potato chunks into a large bowl. Add the olive oil and toss gently to coat. Drizzle with the prepared Vinaigrette, adding just enough to lightly coat the potatoes (you will not not use all the Vinaigrette).
Transfer to a serving bowl. Sprinkle with parsley, chives, and marjoram.
Give the potatoes a gentle toss before serving. I like to serve these just warm or at room temperature.
Place the extra Vinaigrette on the table to add if desired.
Makes 4 to 6 servings.
4 tablespoon extra-virgin olive oil
1 tablespoon sherry wine vinegar
1 teaspoon Dijon mustard
1 garlic clove, finely minced
Coarse salt or sea salt and freshly-ground black pepper
In a small jar with a tight-fitting lid, add the olive oil, wine vinegar, Dijon mustard, garlic, salt, and pepper; shake well and set aside until ready to use.