Creamy chicken with cheddar biscuits

Ingredients

• 1 1/2 cups milk
• 2 tbsp chopped fresh thyme
• 1 tsp salt
• 4 skinless, boneless chicken breasts , cut into bite-sized pieces, about 1 kg
• 1 tbsp vegetable oil
• 1 small sweet potato , peeled and cut into small cubes
• 1 celery stalk , thinly sliced
• 1/2 red bell pepper , chopped
• 1/2 onion , chopped
• 3 tbsp butter
• 1/4 cup all-purpose flour
• 1/2 cup frozen peas

FOR CRUST

• 1 1/4 cups all-purpose flour
• 2 tsp baking powder
• 2 tsp granulated sugar
• 3/4 tsp salt
• 3 tbsp cold unsalted butter , cubed
• 3/4 cup grated old cheddar
• 1 egg
• 1/4 cup milk