Pre-cook the beetroot, this can be done ahead of time. Top and tail the beetroot (don't throw away the beet greens, these can be sautéed similar to silverbeet and used in a filo pie).

Place the whole beetroot into a saucepan and cover with water. Bring to a simmer and cook, covered, for 40-50 minutes until a knife glides into the flesh. Cool the beetroot in the cooking liquid. 

Once the beetroot is cool, rub off the skins, reserving the cooking liquid. Grate one to two of the cooked beetroot to make one cup (lightly packed) grated beetroot – for the burger patties.

Cut the remaining beetroot into 5mm thick slices. Layer into a jar, add the balsamic vinegar and top up with the cooking liquid. Add a generous pinch of salt, cover, and store in the fridge for up to five days. 

To make the burger patties combine the grated beetroot, mince, gherkin, caraway and egg in a bowl. Mix until just combined – don't over-mix or the meat can toughen. Season well, make a small patty and cook in a frying pan to check seasoning, and adjust if needed. Form the remaining mixture into 8-10 patties. Cover and refrigerate until ready to cook. 

Preheat a barbecue grill and lightly oil. Cook patties until golden on both sides and cooked through, about 12-15 minutes. Serve the burgers platter-style with the prepared beetroot slices, buns and extra fillings of choice.