Coarsely grate the potatoes onto a clean tea towel, then squeeze out the excess liquid by twisting the towel. Transfer potato to a bowl. Add egg and sage and stir to combine. Season.
Heat oil in a heavy-based frying pan. Add large spoonfuls of the mixture for 2-3 minutes or until golden and crisp, then turn and cook for a further 2-3 minutes. Fry extra sage leaves until crisp to garnish. Serve.
To cook a larger version, spread all of the mixture into the pan and cook for 5 minutes or until golden underneath. To turn over, slide it out of the pan onto a plate. Place pan over plate and turn both over. Remove plan and cook second side until golden. Cut into wedges to serve