Preheat oven to 180C/350F.

Heat oil in a deep heavy based skillet or dutch oven over high heat. Add chicken and cook until just cooked - it's fine if it's still raw inside. Remove chicken into a bowl. (Note 2)

Reduce heat to medium and melt butter. Add garlic and onion and saute for 5 minutes until onion is translucent. Add flour and cook for 1 minute.

Pour in half the milk and whisk it in so the flour butter mixture melts. It should thicken quite quickly - around 30 seconds. Pour the remaining milk in, whisking constantly, then add the water, salt and pepper.

Turn the heat up to medium high and cook, whisking occasionally, for around 3 to 5 minutes until you start seeing steam rising from the white sauce when you whisk it.

Add the macaroni and chicken, stir, then top with broccoli.

Place the lid on and bake for 20 minutes.

Remove from the oven, switch oven to broiler/grill on high.

Remove lid (Note 3), stir through cheese, then sprinkle over panko and parmesan. (Will still look bit watery at this stage).

Place pot under the broiler/grill for 5 minutes, or until top is golden.

Remove, then let it stand for 5 minutes before serving (sauce thickens quickly).