Place the biscuits in a food processor and pulse until they turn into fine crumbs (alternatively, use a rolling pin to crush them). Combine them with the melted butter, then transfer the mixture to the tart tin and press firmly and evenly into the base and sides to form a tart shell (use a flat bottom cup or ramekin to help you with this). Refrigerate the base while you make the filling.
In a small saucepan combine the cream, vanilla and spice. Heat slowly until just beginning to simmer. Remove from the heat and add in the chopped chocolate and pinch of salt. Stir until the chocolate is melted and you have a smooth, silky ganache.
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.
Add the whole pitted cherries to a small bowl. Once the syrup has cooled, strain it over the cherries and toss to coat. Spoon the cherries and syrup over the tart just before serving.
