Preheat the oven to 190oc.Slice the bottom off the cauliflower so that it sits in an oven proof dish.
Mix the softened butter, shallots, white wine vinegar and mustard with some salt and pepper.
Brush over the cauliflower using all of the mixture.
Cover with foil and place in the oven for 30 minutes.
Remove from the oven and spoon some of the sauce from the base of the dish back over the cauliflower to baste it. Pour over the double cream and place back in the oven for ten minutes.During this time mix together the cheeses.
Remove from the oven and remove and discard the foil.
Sprinkle over the cheeses followed by the breadcrumbs and place back in the oven for a final 20 minutes until tender and the cheesy topping golden and bubbly.
Notes
Optional: Serve the nachos with the sauces and some cooked crispy bacon and grated cheese sprinkled on top.Tip:If not serving immediately, place into a bowl, place a stone from one of the avocados in the middle and cover with cling film.