STEP 1: Pre-heat your oven to 180°C. Break down the cauliflower and broccoli into medium size florets, put into a baking tray and drizzle with olive oil, season with salt & pepper and sprinkle across the paprika. Mix well so the seasoning, spices and oil are well combined. Place into the pre-heated oven and roast for 15-20 minutes until it starts to colour.
STEP 2: Meanwhile, wash and slice your leeks. In a medium pan melt 30g of butter and add in your chopped thyme. Once the butter has melted and the thyme has started to flavour the oil, this should only take about 30seconds, add your leeks to sweat and soften.
STEP 3: To make the cheese sauce you need to start by making a roux. To do this, add 140g of butter to a large non-stick pan and melt. Once melted add 100g of plain flour and mix to create a paste. You want to cook this out for about 5 minutes, this will ensure you don't get a floury taste in your cheese sauce.