Melt the chocolate in a heatproof bowl set over a pan of simmering water, making sure the bowl doesn’t touch the water. Alternatively, do this in the microwave in 30-second bursts. Spoon 1 tsp chocolate into each case, then freeze for 10 mins before adding a spoonful of walnut butter. Push in a few pieces of chopped date, then spoon over the remaining melted chocolate. Freeze for at least another 30 mins, or until the chocolate is firm (the walnut centre will remain gooey), then transfer to a freezerproof container. Will keep frozen for up to a month.