Comforting Chicken Shepherd's Pie with Mashed Potato Topping

Ingredients

• 2 pounds boneless, skinless chicken breasts or thighs
• Salt, to taste
• Black pepper, to taste
• 3 cups chicken broth
• 4 tablespoons unsalted butter
• 1/2 small yellow onion, finely diced
• 3 cloves garlic, minced
• 1/2 teaspoon onion powder
• 1/2 teaspoon mustard powder
• 1/2 teaspoon dried thyme
• 1/2 teaspoon dried rosemary
• 1/4 teaspoon ground sage
• 1/4 teaspoon ground black pepper
• 1/3 cup all-purpose flour
• 1/2 cup half-and-half
• 1 chicken bouillon cube or 1 teaspoon chicken base
• 1 teaspoon Worcestershire sauce
• 2 cups frozen mixed vegetables (peas, carrots, corn)
• 5 cups warm mashed potatoes