Chicken Pot Pie

Ingredients

• 3 tbsp unsalted butter
• 1 onion , finely chopped
• 3 carrots , peeled and sliced into half moons
• 1 tbsp coarse-grain mustard
• 1/4 cup all-purpose flour
• 1 cup reduced sodium chicken broth
• 1 cup milk , plus 1 tbsp for top
• 3 cups chopped cooked leftover chicken
• 1 cup frozen peas
• 1 tbsp dried parsley , or thyme
• 1 tsp salt
• 1/2 tsp black pepper
• 1/2 of 397 g frozen puff pastry , thawed
• 1 egg
• 2 tbsp toasted sesame seeds , optional