Preheat the oven to 180C/350F/Gas 4. Line two baking trays with baking parchment then oil a thickish handle of a wooden spoon and lay it on a cooling rack.
Measure the butter, sugar and syrup into a small, heavy-based pan. The easiest way is to measure the butter, then the sugar on the scales (in the pan if you have digital scales), then measure the syrup on top to make up to 165g/6oz total weight.
Heat gently until the butter has melted and the sugar has dissolved. This will take about 15 minutes over a low heat. Don’t let the mixture boil as it may crystallise. To check when the sugar has dissolved, stir occasionally, pulling the spoon across the bottom of the pan until you can no longer hear the gritty granules being scraped along and most of them have disappeared.
Leave the mixture to cool slightly, about 2-3 minutes, then sieve in the flour and ginger. Pour in the lemon juice and stir well to mix thoroughly. Drop four teaspoonfuls of the mixture onto each of the prepared baking trays to make neat circles, about 10cm/4in apart.
Bake in the pre-heated oven for about 10-15 minutes, or until the mixture is well spread out, looks lacey and is a dark golden colour. Once baked, you need to work fast to shape the brandy snaps, so its easier if you bake one tray at a time. Remove each tray from the oven and leave for a minute or so to firm up slightly, then lift from the baking parchment using a fish slice. The mixture needs to be just firm enough to remove, but pliable enough to shape. Check by releasing around and under the edges with a small palette knife.
Quickly roll a circle of the warm mixture around the handle of the wooden spoon, having the join underneath. Press the join lightly together to seal, then slide the brandy snap off the spoon and leave it to firm up on the wire rack, again with the join underneath. If any of the circles on the sheet harden too much to work with, put them back in the oven for a few seconds to soften again. Repeat until all the mixture has been used. If the mixture in the pan becomes too firm to drop in neat spoonfuls, roll a teaspoonful of it into a small smooth ball in your hands, sit it on the baking tray and flatten slightly with your fingers. When cold, store the brandy snaps in an airtight tin or container; they will keep for at least a week.