Preheat the convection oven to 100 degrees, in the normal oven to 125 degrees. Cover one or two baking trays with parchment paper (several trays can be pushed into the oven at the same time if the air is circulated).
Halve the tomatoes horizontally or cut into approx. 7 mm thick slices, depending on their size. Distribute with the cut surface upwards with a little space on the sheet. Sprinkle with sugar and picked herbs. Season with salt and pepper.
Push the tray - or the trays - into the oven and dry the tomatoes with the steam flap pulled out (or hold the door ajar with a skewer). Depending on the variety, size, degree of ripeness and method, the process takes 90 minutes to six hours.
As soon as the tomatoes have visibly shrunk (the edges contract and the juice has evaporated), remove them and leave to cool on a rack.
Can be kept for three days in the refrigerator in a resealable plastic container or around six weeks in the freezer. The tomatoes must be dry through and through for longer storage. Store in a cool, dry place in a paper or plastic bag.