Step 1

Preheat the grill to medium high.

Step 2

In a medium size bowl, add the minced shallot, vinegar, salt, tarragon and mustard. Add olive oil in thin steady stream whisking as you pour to emulsify. Set it aside.

Step 3

Place the potatoes in a large piece of aluminum foil, drizzle with 1 tablespoon of the olive oil, 1/4 teaspoon of the salt, and 1/4 teaspoon of the pepper. Then fold and seal the potatoes, as if creating a large aluminum foil package or envelope. Put it directly on the grill and cook for 30 minutes, flipping it once.

Step 4

In a large bowl, season the radicchio with the remaining 2 tablespoons of olive oil, 1/4 teaspoon salt, and 1/4 teaspoon pepper. Grill the radicchio for about 3 minutes per side. Remove from the grill and cut it into 1/2-inch slices.

Step 5

Remove the potatoes from the grill, opening the package carefully as the steam will be piping hot. Transfer to a salad bowl, combine with the cut radicchio and toss with the prepared vinaigrette.