Preheat the oven to 425° F. Line a large baking sheet with parchment paper or foil.
Wash the red potatoes, then slice them into 1-inch pieces. Slice the shallot into rings.
Toss the sliced potatoes and shallot in a large bowl with the vegetable oil, ½ teaspoon of salt, and ½ teaspoon of pepper. Once everything is combined, spread the potatoes and shallots on the prepared baking sheet.
Place the pan in the oven for about 25 minutes, until the potatoes are tender and beginning to brown on the edges.
Remove the pan from the oven and allow the potatoes and shallots to cool to room temperature.
Make the dressing:
While the potatoes roast, make the dressing. Place the parsley, tarragon, anchovies, and garlic into the bowl of a food processor or mini chopper.
Run the chopper or food processor until everything is finely minced. Pour some of the buttermilk in with the herbs if necessary to help everything blend up well.
Scrape the herb mixture into a large bowl. Add the salt, pepper, mayonnaise, buttermilk, vinegar, and chopped scallions to the bowl.
Whisk the dressing until the mixture is smooth, and all ingredients are combined.
Finish the salad:
Add the cooled, roasted potatoes and shallots to the dressing. Gently stir them into the dressing until they're coated completely.
Transfer the potato salad to a serving bowl and garnish with the snipped chives.
The salad can be served immediately or it can be chilled first in the refrigerator. Store any leftovers in the fridge for up to 3 days.
Makes about 7 cups.
Notes
Look for fresh parsley and tarragon in the produce section with other fresh herbs. Or, get them from farmer's markets, local growers, or your own garden.
Not an anchovy fan? Don't worry: anchovies don't make this salad taste fishy. They add a little salty, umami flavor that nicely boosts the fresh herbs and tangy buttermilk in the dressing.
You can use baby red potatoes or regular red potatoes for this salad—whichever you use, make sure to slice them to a consistent size of about one to one-and-a-half inches.