Preheat your oven to 200°C (390°F). Line a baking sheet with parchment paper and set aside.
Toss the cauliflower florets with olive oil, salt, and pepper until evenly coated. Spread them out in a single layer on the prepared baking sheet.
Roast the cauliflower in the oven for 20-25 minutes, shaking the pan halfway through, until they are golden and slightly charred around the edges. The aroma should be nutty and inviting.
While the cauliflower roasts, melt the butter in a saucepan over medium heat. Add the flour and stir constantly for about 1-2 minutes, until the mixture turns a light golden color and smells slightly nutty.
Gradually whisk in the milk, stirring continuously to prevent lumps. Cook for 3-4 minutes until the sauce thickens to a creamy consistency.
Remove the sauce from heat and stir in the shredded cheddar until melted and smooth. Season with a pinch of salt and black pepper to taste.
Transfer the roasted cauliflower to a baking dish, spreading it out evenly. Pour the warm cheese sauce over the cauliflower, ensuring all pieces are coated generously.
Mix the breadcrumbs with smoked paprika, then sprinkle evenly over the top of the casserole for a crispy, smoky finish.
Bake the assembled dish at 180°C (355°F) for 15-20 minutes, until the top is bubbling and golden brown.
Remove from the oven and let rest for 5 minutes. The cheese will set slightly, making it easier to serve.
Serve hot, garnished with a sprinkle of black pepper if desired. Enjoy the smoky, cheesy goodness with crispy edges and tender cauliflower inside.