Stew the cherries gently with 1 tablespoon of water, half the sugar and 2 tablespoons (30 g) of the butter, until they are soft and have made some juice. Allow the cherries to cool a little and then stone them.
Butter the bread. Put 4 slices, butter side down, in a shallow fireproof dish. Pour in the cherries and their juice. Sprinkle with 2 tablespoons (30 g) of the remaining sugar. Put the 4 remaining slices of bread butter side down over the cherries. Sprinkle with the remaining sugar and dot with the remaining butter. Bake at 400°F (200°C, Gas Mark 6) for 15 minutes. Serve immediately.