Preheat the oven to 340 degrees F / 170 C.
Melt the butter in a medium pot over a medium-low heat.
When melted sprinkle in the flour and stir to combine, cook on low heat for 2 minutes.
Add ¼ cup of milk at a time, stirring in between each addition to ensure there’s no lumps.
When all the milk has been added continue to cook for another 2 minutes, stirring continuously.
Add the cheddar cheese, nutmeg, salt and pepper. Stir for 3-4 minutes until well combined and cheese is fully melted, adjust seasoning to taste. Remove from the heat.
In a large oven dish add the vegetables in an even layer, cover with the cheese sauce, stirring gently to ensure the vegetables are coated in the sauce.
Sprinkle the panko crumbs and parmesan cheese over top of the vegetables.
Bake in the oven for 30-35 minutes. The topping should be a lovely golden color and the vegetables should be tender.
If the vegetables need to be cooked a little longer cover the baking dish with foil and continue to cook for a further 5-10 minutes until completely cooked through, do not over cook.
Serve immediately or store leftovers in the fridge for up to 4 days.