In a double boiler:  Melt 1 T butter.
Add 1 c(ish) beer or ale (best with dark beer).
Warm.

Mix 1 lb (ish) shredded sharp cheddar (sharper the better) w/ 2 tsp cornstarch.

Add to beer.  stir until melted.  Add one beaten egg or egg yolk slowly.  Season to taste with good mustard and worcestershire sauce.  stir until hot.  serve on toast or with dipping chunks of bread.  Also good with yorkshire pud and sausage.