Serve this grilled dinner family-style on a big platter, and let everyone help themselves. You can marinate the chicken up to 30 minutes, if desired. *Cook time does not include marinating the chicken*
Mix together vinaigrette ingredients: In a small bowl or jar, combine white-wine vinegar, Dijon mustard, and honey; season generously with coarse salt and ground pepper. Whisk or shake to combine. Add olive oil; whisk or shake again. Store in an airtight container or jar, and refrigerate, up to 2 weeks. Shake before using.
Heat grill to medium. Fold two 4-foot-long sheets of aluminum foil in half to make two separate double-layer sheets. Place half the potatoes on each double layer. Form two packets, folding foil over potatoes and crimping edges to seal. Place on grill and cook, turning over once, until potatoes are tender, about 25 minutes. Remove from heat. Leave potatoes wrapped in foil to keep warm. Raise grill to high; lightly oil grates.
Meanwhile, make marinade: In a large baking dish, whisk together oil, garlic, vinegar, thyme, 1 teaspoon salt, and 1/2 teaspoon pepper. Add chicken; turn several times to coat. Let marinate at room temperature 10 minutes and up to 30 minutes.
Lift chicken from marinade and grill until browned and cooked through, 2 to 3 minutes per side. Remove from grill. Cover chicken with foil to keep warm.
Remove warm potatoes from foil; transfer to a medium bowl, toss with butter, and season with salt and pepper. In a medium bowl, toss asparagus with 2TBS Vinaigrette. Serve the grilled chicken with potatoes and asparagus. Garnish with thyme sprigs, if desired.