Christas is typically 38-42 degrees and very humid. If you're lucky, Christmas will be outside on a terrace or preferably in someone's garden. Christmas Eve begins around 8pm while the sun is still up and it's roasting hot. Despite this, they still have loads of cooked meat. However sides (including the meat sides, like vitel thone) tend to be all cold. Roast potatoes english style are a lovely idea but probably not the time of year for it! What I did do one year which people enjoyed, but which you definitely need good fridge access as it can't stay out in the heat a moment, is trifle. In fact I've actually thought maybe to make an ice cream trifle one year. Much more appropriate to the weather. Maybe go for an Eton mess. Argentines have a very sweet tooth, and with the heat of Christmas I'd look towards doing either a savory cold dish (they love their 1970s Russian Potato Salad complete with canned peas here, you could try doing an actual modern potato salad and see if it's accepted! Alternative would be an update to that other 70s classic, shredded carrot and raisins salad...) or go for a cold dessert. Do not think English christmas, though they do like a horribly dry fruitcake here as well. Maybe have a look through some Australian recipe sites for some inspiration, their menu will be more weather appropriate!