Preheat the oven to 200°C. Lightly grease a medium-sized gratin dish.
Cook the cauliflower florets in plenty of lightly salted boiling water for about 4 minutes, or until bite-tender. Drain well and set aside
In a medium-sized heavy-based saucepan, melt the butter over a low heat then stir in the flour to form a roux. Allow roux to cook gently, stirring continuously until lightly golden.
Add milk and cream to roux, about a cup at a time. Whisk continuously, until all the milk and cream have been added. Cook until the sauce is thick enough to coat the back of a wooden spoon.
Remove from the heat and stir in the grated cheese and season with salt. Stir in the cooked cauliflower.
Spoon into the gratin dish and top with breadcrumbs and crumbled Puhoi Valley Kawau Blue cheese.
Place on a shallow oven tray in the oven and cook until golden and bubbling hot.