This makes a baking trayful:
2 slices bread, and the same weight of flour, cheese and butter. Any kind of bread; plain flour (wholemeal is fine) and any kind of cheese, but the stronger-tasting the better.
Whizz in food processor until beginning to come together, knead lightly and roll out. Stamp out with cookie cutter, bake on greased baking tray at Mark 5, 180 (fan oven) or 190 (non fan) for 15 minutes.
Edited to add: Forgot to say you can season this with Tabasco and/or dried chilli flakes, 1/4 tsp dry mustard powder, and a sprinkle of dried mixed herbs. And, of course, you can scale up the quantities really easily - the idea is equal quantities of bread, flour, butter and cheese!