Cook the potatoes in a large pot of boiling salted water until just fork-tender, add the peas at the end and leave them to cook for 2 minutes,  then drain well – try to time the potatoes and peas with the cheese sauce.  In a large skillet, melt the butter and then whisk in the flour, salt and pepper.  Continue to whisk for a minute or 2 until it starts to brown just a touch, then start slowly drizzling in the milk – keep whisking!  Once all of the milk is in, continue to whisk as you bring the mixture to a boil and once it thickens a bit, assess whether or not you need more milk.

When the white sauce is hot, thick enough to your liking, and the potatoes and peas are draining, remove the skillet from the heat and stir in the cheese until melted.  Pour the potatoes and peas into a large serving bowl, and cover them with the hot cheese sauce – these go great with everything!