Heat the clarified butter in a wide, heavy-based pan to 160°C. Meanwhile, peel and grate the potatoes, working quickly or they will start to oxidise and discolour. Season the grated potatoes, then add them to the hot butter. Fry for five to eight minutes or until almost tender, stirring and moving the potatoes around the pan frequently to prevent them from sticking to the bottom and burning.
Tip the potatoes into a colander or sieve set over a large bowl. Leave to drain for about 10 minutes, then season the potatoes with salt and pepper to taste (discard the butter drained into the bowl). Spread out the potatoes in a thick layer on a baking tray lined with baking parchment – you want a 2cm thick layer once the potatoes have been pressed. Place another sheet of baking parchment on top, then weigh down with another heavy baking tray. Chill for at least an hour (or overnight if preparing in advance) until firmly pressed.
When ready to serve, heat oil for deep-frying to 180°C. Slice the chilled pressed potato into ‘chips’ 5cm long, 2cm wide and 2cm thick. Deep-fry for a few minutes until golden and crisp. Drain on a tray lined with kitchen paper, then dust with a little salt and vinegar powder.
To make the powder, simply mix the two ingredients together. Store in a salt shaker (or an airtight container, if making in advance).
To make the taramasalata, tear the bread slices into smaller pieces directly into a food processor. Add the cod’s roe, peeled garlic and milk. Blitz the ingredients together. With the machine running, gradually trickle in the oil. Once the mixture has emulsified, add lemon juice to taste. Spoon into a piping bag fitted with a plain round nozzle and keep in the fridge until needed.
Pipe three dots of taramasalata on each fried ‘chip’ and garnish each dot with a frond of bronze fennel. Serve immediately.