Wash the rosemary, dab dry and pluck the needles from the twigs. Wash thyme, dab dry and pluck the leaves from the stems. Wash the potatoes thoroughly and cut them in half lengthwise.
Brush the baking tray with olive oil, spread the herbs evenly on top and place the potatoes on the baking tray with the cut edge facing down (directly on the herbs). Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 30-35 minutes.
Meanwhile peel garlic and chop very finely. Put the egg, mustard and garlic into a tall mixing bowl and beat. Let the oil run in slowly while stirring constantly. Add the olives to the potatoes on the baking tray 3-5 minutes before the end of the cooking time.
Arrange potatoes, olives and Parma ham on a plate. Serve garnished with oregano, rosemary, parsley and thyme. Add aioli to taste with slices of roasted garlic extra.