Apple cider turkey pot pie

Ingredients

• 2 tbsp cornstarch
• 2 cups apple cider , divided
• 1 sweet potato , peeled and cut into 1/2-in. cubes
• 1 onion , chopped
• 1/4 cup 35% cream
• 2 tbsp Dijon mustard
• 1/2 tsp dried sage
• 1/2 tsp salt
• 1 kg skinless, boneless turkey breast , cut into 1/2-in. cubes
• 1 cup frozen peas , thawed
• 1/2 450-g pkg frozen puff pastry
• 1 egg yolk , beaten