Porter-Braised Chicken With Root Vegetables

Ingredients

• 8 skinless or skin-on chicken thighs (about 3 1/2 pounds total)
• salt and freshly ground black pepper to taste
• 2 tablespoons canola oil
• 2 tablespoons plus 5 tablespoons unsalted butter, at room temperature
• 2 medium yellow onions, chopped
• 4 medium carrots, peeled and cut into 1-inch chunks
• 4 to 6 medium red potatoes, peeled if desired, cut into 1-inch chunks
• 1 medium (about 14 ounces) celery root, peeled, trimmed, halved, and cut into 1-inch chunks (or substitute potatoes)
• two 12-ounce bottles porter
• 2 cups homemade chicken stock or low-sodium chicken broth
• 2 tablespoons packed light brown sugar
• 2 tablespoons dijon mustard
• 2 teaspoons tomato paste
• 1 teaspoon dried thyme
• 1/4 cup all-purpose flour