Pour over enough ganache to cover the base of the tart shell. Add the cherries, cut side down, in an even layer. Pour the remaining ganache over the top and smooth with the back of a spoon. Return to the fridge to set. To make the syrup, simmer the juice and sugar until the liquid has thickened and reduced by half, about 15 minutes. Add the spice and simmer for 2 more minutes. Remove from the heat to cool.
