Melt the butter in a small saucepan. Once the butter has melted, add the flour and fry briefly. This is called making a roux.
Make sure not to turn the heat up too high, and don't let it change color. It's okay if it "sweats" a little. The butter and flour will then bubble gently.
Next, add the cream and milk, and bring the mixture to a boil. Whisk until the sauce thickens.
Add the gorgonzola in pieces and let it melt into the sauce. Season the sauce with salt and pepper.
Finally, sprinkle some extra gorgonzola on top and serve immediately. Bon appétit!