1st job - find a recipe. Ought to be easy surely, especially with a shelf stuffed with cookery tomes like mine, but was there a rarebit to be seen? Was there buggery. After 20 minutes fruitless searching - including checking the index of "Winning Ways With Cheese" at least 3 times thinking 'if any book will have it surely this one must' I remembered the 'Welsh' part of the name and thereafter things moved rather more swiftly on. ;-)
I adapted the recipe from WWwC - incidentally a fantastic book - so very very of it's time. It's beautifully photographed in 1980's brown and orange and features a somewhat younger and frillier Mary Berry as the judge of what was the tie-in title to a National Cheese Board competition. Brilliant piece of social history! You probably wouldn't make a lot of the recipes though... [Incidentally I remember that Union Jack made of cheese logo with great fondness. Todays British Cheese Board seem to have done away with it. :-( ]
Rarebit - the Welsh one [This makes a fair bit - enough for a whole short baguette sliced in half and another roll.]
1tsp wholegrain beer mustard / your favourite
0.5tsp worcestershire sauce
1tbsp beer (actually I must admit to using lager as that's what was about)
4oz grated tasty chedder / cheese of your choice
Tomato - sliced [optional]
Mix everything bar the tomato together. That's kinda it - other recipes fiddle about with roux and eggs and what have you but this is pretty simple and adaptable I think. I may try it with mushroom ketchup in place of the worcestershire sauce next time.
Anyway - what I did with mine was use it on part baked baguettes; as I baked them off I sliced a large vine tomato, sprinkled the slices with a little salt and pepper and chucked in the oven for 5ish mins. [Watch the salt as mature cheese can be surprisingly salty I find. It helps draw the juices out of the tom though so I think you need a bit.]
Slice baguettes in half, lay tom slices on, cover with cheese mixture and pop under the grill to melt.