Up to a day ahead, heat oven to 200C/fan 180C/gas 6. Slice the ciabatta into about 25 thin slices. Lay them on a couple of baking trays and brush with the oil. Toast in the oven for 10 mins until they begin to go golden, checking after 5 mins as the trays may need turning.
Up to an hour ahead, cut the stilton into slices a little smaller than the toasts (this is easier to do if the cheese is cold from the fridge), keep covered.
Before serving, heat oven to 200C/fan 180C/gas 6. Spoon a little pile of beetroot onto the end of each piece of bread. Prop a slice of cheese up against each pile of beetroot and bake for 3-4 minutes until the cheese is starting to melt. You don’t want it too melty – try to catch it just as it’s starting to ooze over the edge.
Top each cheesy canapé with a little sprig of celery leaves and serve immediately.