Wash the cherries and remove the stalks. Put in a bowl and lightly crush, so the skins pop but the fruit retains its shape. Add 2 tbsp caster sugar and the kirsch, toss together, cover and leave to macerate for two hours.
Preheat the oven to 180C/gas mark 6. Grease a baking dish just wide enough to hold the cherries in one layer, and add half the demerara sugar. Spin the dish round to coat the inside with demerara, then set aside.
Sift the flour into a mixing bowl and add a pinch of salt and the remaining caster sugar. Whisk in the eggs, followed by the milk and melted butter, until you have a smooth batter. Stir in the almond essence, if using, and the lemon zest, then tip in the cherries and their juices.
Pour into the prepared baking dish and bake for about half an hour, until just set but still a bit wobbly. Sprinkle with the remaining demerara sugar and serve warm, rather than hot.