Fill a medium saucepan with 1 inch of water. Place steamer basket on pan; bring water to a boil over high. Place eggs in steamer basket; cover, and cook 14 minutes. Remove eggs from basket, and place in ice water or run cold water over eggs for 5 minutes. Peel eggs, and cut in half lengthwise.
Preheat oven to 400°F. Combine potatoes and 1 tablespoon of the oil on a rimmed baking sheet; toss to coat. Sprinkle with 1/4 teaspoon each of the salt and pepper. Roast, stirring once, until well browned and tender, about 20 minutes.
Whisk together vinegar, shallot, mustard, cornichons, and remaining 3 tablespoons oil, 1/2 teaspoon salt, and 1/4 teaspoon pepper in a large bowl. Add hot potatoes, kale, and snap peas; toss to coat and allow kale to soften. Place potato mixture on a platter. Top with radishes, parsley, and egg halves.