Heat the oven to 200c/fan 180c/gas 6. Push a metal skewer lengthways and close to the base through one potato at a time. Slice downwards every couple of millimeters with a sharp knife and pull out the skewer when you’ve finished. If you are confident that you can slice through without cutting all the way through then you can skip using the skewer.
Put the potatoes cut side up into a roasting tin and slosh over some oil, rubbing it into the potatoes. Season well. Roast for 50 minutes. Mix the dill, crumbs and lemon zest with some seasoning and sprinkle this over the potatoes, roast for another 10-20 minutes or until the potatoes are tender and the crumbs are browned.