Roast the potatoes until the sides touching the pan are golden brown, about 25 minutes. Flip them and roast for 10 minutes.
Add the asparagus and roast until it is crisp-tender, about 6-8 minutes.
To make the vinaigrette, whisk the garlic, mustard, parsley, chives, salt, pepper, lemon juice and oil in a bowl big enough for the potatoes and asparagus.