Boil from cold: Put the potatoes in a pan of cold salted water, bring to the boil, then simmer for 15 to 18 minutes until tender. Starting cold stops the outsides falling apart.
Dry them: Drain and leave the potatoes to steam-dry for 5 minutes, so they crisp rather than steam.
Press flat: Sit each potato on a board or tray and press down with a glass or masher to about 1cm thick, keeping them whole.
Crisp: Heat the olive oil and butter in a large pan over a medium-high heat. Add the potatoes, garlic and thyme, and fry for 5 to 6 minutes a side until deep golden and crisp.
Season and finish: Season well, and scatter over the grated cheese to melt, if using. Serve hot.
