Chicken Pot Pie Biscuits

• 6 tablespoons butter

• 1 onion, finely chopped

• Salt and pepper

• 5 tablespoons plain flour

• 1 sprig fresh thyme, leaves removed

• 1 sprig rosemary, leaves removed

• 3 cups chicken stock

• 2 chicken breasts

• 1 cup milk

• 1 large potato, diced and blanched

• 1 cup frozen peas, defrosted

• 4 sheets puff pastry

• 1 egg, beaten