Cook the potaotes in a big pan of water until soft. Drain well. Place the pan back on the heat. Melt the butter and cook the garlic for 1 min to soften, then stir inthe milk and heat through. Return to the potatoes to the mash until smooth.
Heat the oven 180c/fan/160/gas4. Spoon the mixture into a 20x30cm baking dish.
Sprinkle the breadcrumbs , cheese and thyme over the top.
If making for the freeze, freeze at this stage.
Cook for 15 mins until the crumbs are crisp and the cheese has melted.