How to Make It
In a small skillet, bring the vinegar, peppercorns, allspice, juniper berries, bay leaf and clove to a boil. Remove from the heat, add the shallot and let cool. Strain the vinegar; reserve the shallot and 1 tablespoon plus 1 teaspoon of the vinegar. In a small bowl, whisk the reserved vinegar with the mustard and 3 tablespoons of the oil. Season with salt and pepper.
Steam the potatoes over boiling water until still slightly firm, about 10 minutes. Let cool; cut each one into 6 wedges.
Heat the remaining 2 tablespoons of oil in a large cast-iron skillet. Add the potatoes and cook over moderate heat, turning once, until golden and cooked through, about 10 minutes. Remove from the heat. Top the potatoes with the Fontina and let melt. Add 2 tablespoons of the vinaigrette to the skillet and swirl to coat.
In a large bowl, toss the reserved shallot slices with the watercress and the remaining vinaigrette. Transfer the salad to a platter, top with the potatoes and cheese and serve at once.