Heat a frying pan over a medium heat. Add your chicken breasts and fry off for a couple of mins until golden, crisp and tender. Remove from the pan.
Add your butter to the pan. When melted, add your garlic and cook out for 1 minute.
Add your flour, cook out for 2 mins, then gradually pour in your milk in small increments, whisking all the while until you have a smooth sauce.
Once all the milk has been added, bring to a boil then simmer for 2 mins until thickened. Add your cheddar, mozzarella, salt and pepper. Stir until your cheese melts.
Pop your chicken back in the pan along with your broccoli and stir until everything is coated.
Mash your cooked potatoes either in a potato ricer or with a potato masher.
Stir through spring onion, and salt and pepper until totally combined.
Pour your chicken and broccoli mixture into a dish and spread your potatoes on top.Sprinkle mozzarella cheese over the top, then take to the oven to bake for 25 minutes.
