Wash the sweet potatoes and cover and cook in lightly salted water for about 10 minutes over medium heat. Drain the potatoes, let them cool down a little and peel them. Preheat the oven top and bottom heat to 175 °.
Butter a flat baking dish. Cut the sweet potatoes into 1-2 cm thick slices and lay out a roof tile in the prepared shape.
Put the sugar and orange juice in a small saucepan, add the sugar
Melt over low heat. Stir in butter and let it melt too.
Drizzle this syrup over the potatoes and bake everything in the oven (center, gas mark 2, fan 160 ° C) for about 20 minutes.