Preheat the oven to 375 degrees. Place the cauliflower florets onto a parchment lined baking sheet. Drizzle with olive oil and season well with salt and pepper. Sprinkle breadcrumbs over top and bake for 25 - 30 minutes until the cauliflower is tender and crisp.
Melt the butter in a saucepan on medium heat. Whisk in the flour and cook for 1 minute while stirring. Gradually whisk in the milk until smooth. Continue whisking until it is thick and smooth.
Add in the shredded cheese and whisk until smooth. The sauce should be smooth and thick. Season with salt and pepper to taste. (If the sauce is too thick and clumpy thin it out with a little more milk)
Spoon the cheese sauce over the cauliflower to serve.