Can this be made in advance for a dinner party? If so, through what step?

Yes, I'd like to come to the party too. ;0) The beauty of mac & cheese (one of the beauties) is that it's a perfect make ahead dish.

That's a party I'd like to go to! I've refrigerated similar mac and cheese dishes for up to 2 days but don’t add the panko and parmesan topping until you’re ready to put it in the oven. You might want to let it come to room temp before baking or the baking time might take a little longer.