Pat chicken dry. Season with salt, pepper, paprika, and thyme.
Whisk Dijon, honey, whole-grain mustard, vinegar, broth, and garlic in a bowl.
Heat olive oil in a large skillet over medium-high. Sear chicken until golden on both sides. Transfer to a plate.
Pour the honey mustard mixture into the pan. Scrape up browned bits and bring to a gentle simmer.
Nestle chicken into the sauce. Reduce heat and simmer until cooked through, 10–12 minutes, to 165°F.
Stir cornstarch with water. Drizzle into the skillet and simmer 1–2 minutes to thicken as desired.
Turn off heat and swirl in butter. Rest 5 minutes, then garnish with parsley and serve.