1.Preheat oven to 220°C/425°F.
2.Place ham on an oven tray; cook, uncovered, until browned lightly.
3.Meanwhile, peel and coarsely grate potatoes; squeeze out as much excess liquid as possible. Combine potato and egg white in a large bowl; divide into eight portions
4.Spray a heated large non-stick frying pan with cooking-oil; place one portion of potato mixture into pan, flatten with a spatula. Cook over medium heat until lightly browned both sides and cooked through. Repeat with remaining potato portions. Cover rösti to keep warm.
5.Cook tomatoes in the same pan until just beginning to soften. Serve rösti with ham, tomatoes and onion.
Wilted baby spinach leaves can also be served with these rösti.Note