Preheat the oven to 180C/350F/Gas 4. Line two baking trays with greaseproof paper.
Melt the butter with the sugar and syrup, stirring over a low heat until the sugar dissolves. Remove the pan from the heat and stir in the flour, ginger, brandy and lemon zest.
Place four scant tablespoons of the mixture onto one of the baking trays, leaving plenty of room for the mixture to spread. Bake in the centre of the oven for 10-12 minutes or until bubbly and deep golden-brown. While the brandy snaps are cooking, grease two wooden spoons with butter and wrap an elastic band around them to bind them together. Place four more scant tablespoons of the brandy snap mixture on the second baking tray.
Take the brandy snaps out of the oven and put the second tray in to bake for the same amount of time. Let the brandy snaps rest for 30-60 seconds, then carefully lift one off with a palette knife and wrap around the spoons, overlapping it a little. Hold for around 30 seconds until the biscuit sets in a tube shape, then gently slide off the spoons and put on a rack to cool. Repeat the method with the remaining brandy snaps. If the biscuits become too hard to roll at any stage, simply return to the oven for a few seconds to soften them. Continue baking and rolling the brandy snaps until all the mixture is used.
To prepare the filling, whip the cream until soft peaks form. Stir in the chopped ginger and spoon into a large piping bag fitted with a plain nozzle. Pipe the ginger cream into each end of the brandy snaps and place them fairly close together on a rack placed over a board.
Melt the chocolate in a heatproof bowl over a pan of gently simmering water, taking care the bottom of the bowl does not touch the water. Remove from the heat and, using a dessert spoon, drizzle melted chocolate over the brandy snaps. Place in the fridge for 15 minutes or until the chocolate sets. Carefully transfer the brandy snaps to a serving plate when you are ready to serve.