Make sure you source a good-quality smoked eel. We buy ours from the Dutch Eel Company in Lincolnshire, which rather surprisingly is the only eel merchant based in the UK. Serving the eel warm with the remaining ingredients at room temperature makes the whole ensemble much more appetising.
Cheltenham beetroot, more correctly Cheltenham Green Top Beetroot, is one of the oldest varieties of this underrated native vegetable. It is long in shape, very sweet and has a fine earthy flavour