3/4 pound purple potatoes
3/4 pound fingerling potatoes
1/2 cup plus 2 tbsp. extra-virgin olive oil
3 tablespoons sherry vinegar
1 tablespoon stoneground mustard
1 teaspoon kosher salt, divided
1/2 teaspoon pepper, divided
2 medium onions, cut into 1/2-in. dice
3 garlic cloves, finely chopped
3 large ears yellow corn, kernels cut off
1 pt. multicolored cherry tomatoes, halved
1 avocado, pitted and diced
1 1/2 teaspoons finely chopped fresh marjoram leaves
1. Bring potatoes to a boil in a medium pot of well-salted water just to cover. Reduce heat and simmer until just soft when pierced (or cut one in half and try it).
2. Whisk 1/2 cup oil, the vinegar, mustard, 1/2 tsp. salt, and 1/4 tsp. pepper in a small bowl.
3. Sauté onions in remaining 2 tbsp. oil until translucent. Add garlic and cook 30 seconds, then add corn and heat until just warmed through. Season with remaining 1/2 tsp. salt and 1/4 tsp. pepper and let cool.
4. Drain potatoes and let stand until just cool enough to handle. Taste a shred of skin; peel if bitter. Cut potatoes into bite-size pieces and toss with 1/2 of vinaigrette.
5. Add cooled corn mixture, tomatoes, avocado and marjoram. Drizzle with remaining vinaigrette to taste and gently mix together.