Baby Potato Salad

• 2 pounds baby Yukon Gold or red-skinned potatoes (about 36), unpeeled (halved if large)

Kosher salt

• 1 large egg yolk
• 2 teaspoons white wine vinegar
• 1/2 cup vegetable oil
• 2 tablespoons spicy brown mustard
• 2 tablespoons chopped fresh chives

1. Place potatoes in a large pot and add cold water to cover by 2 inches; season generously with salt. Bring to a boil, reduce heat, and simmer gently until potatoes are tender, 20–25 minutes. Drain and let potatoes cool slightly. Peel, if desired.
2. Meanwhile, whisk egg yolk and vinegar in a large bowl; season with salt. Whisking constantly, gradually add oil, drop by drop at first, and whisk until mayonnaise is thick and creamy. Whisk in mustard.
3. Add warm potatoes to bowl with mayonnaise and toss to coat; season with salt. Fold in chives just before serving.
4. Do Ahead: Mayonnaise can be made 1 day ahead. Cover and chill.