Step 1

Pour 500ml milk into a large saucepan and add 4 tbsp plain flour and 50g butter.

Step 2

Turn on the heat to medium and start to whisk the mixture. Keep whisking fast as the butter melts and the mixture comes to the boil – the flour will disappear and the sauce will begin to thicken.

Step 3

Whisk for another 2 mins while the sauce bubbles then stir in 100g grated strong cheddar cheese (or 50g grated cheddar, 50g crumbled blue cheese) until melted.