Chicken Pot Pie Casserole - Instant Pot Singapore

Ingredients

• 4 tbsp Butter
• 3 medium Carrots (diced (about 1 1/2 cups))
• 3 stalks Celery (diced (about 1 1/2 cups))
• 1 large Yellow Onion (diced (about 1 1/2 cups))
• 1 tsp chopped fresh Thyme
• 1 tsp Kosher Salt (divided)
• 1/2 tsp freshly grounded Black Pepper
• 4 tbsp All-Purpose Flour
• 2 cups Whole Milk
• 1 cup low-sodium Chicken Broth
• 1 tbsp dijon mustard
• 1/2 tsp Garlic Powder
• 4 cups cooked shredded Chicken
• 1 cup Frozen Peas
• 1 Biscuit Dough (16.3oz tube)