Special Equipment: V-slicer or mandoline, deep-fry thermometer
Wash the vegetables and dry very well. Set aside.
In a small bowl combine the garlic, rosemary and salt. Set aside.
Warm the oil in a large pot over high heat to 180°C.
Trim 2cm off the end of each sweet potato. Using the V-slicer or mandoline, slice the sweet potatoes into very thin slices, about 1/4cm thick. Trim 2cm off the root end of the beets. Using the V-slicer or mandoline slice the beets into very thin slices, about 1/4cm thick.
When the oil is hot add about a quarter of the sweet potato slices. Let fry until golden and the bubbling has almost completely subsided, about 2 to 3 minutes. Using a mesh sieve or slotted spoon remove the chips to a kitchen paper-lined baking tray. Sprinkle with some of the garlic, rosemary, and salt mixture.
Continue with the remaining sweet potatoes. Transfer to a serving plate.
Next, fry 1/4 of the beetroots. Let fry until curled at the edges and most of the bubbling has subsided, about 3 to 4 minutes. Transfer the beets to another kitchen paper-lined baking tray and sprinkle with salt mixture. Continue with the remaining beetroots. Let cool and transfer to a serving plate.