Preheat oven to 400°F. Line a baking sheet with parchment.

In a medium bowl, toss together potatoes, shallot, olive oil, and salt until coated. Transfer to prepared pan. Roast for 30 minutes, or until potatoes are soft and corners are browned.

In a large kettle, combine honey, harissa, roasted vegetables, and stock. Place over medium-high heat and bring to a boil. Reduce heat and simmer for 20 minutes, or until potatoes are very soft.

Transfer to a blender and purée until smooth. Return to pan, add vinegar, and gently warm as needed.

Taste and adjust seasoning with salt and pepper.

Serve with a dollop of sour cream. Sprinkle with chervil.