1. To make the dough, mix all the ingredients in a standing mixer with dough hook attachment or knead by hand until the dough is smooth, elastic and stops sticking to your hands or clears the side of the mixer bowl. Place it in an oiled bowl, cover with cling film and leave in a warm place for 1 hour.
2. To make the roasted peppers, preheat the grill to its highest setting. Prepare a plastic bag large enough to fit the peppers. Place the peppers on a roasting tray lined with foil. Place them as high as possible under the grill and roast for about 5 minutes on each side, turning with tongs, until the skin is charred and blistered all over. Remove them from the grill and put in the plastic bag to sweat, for 30 minutes.
3. In the meantime prepare the sun-dried tomato paste if making your own: blend the tomato halves in a food processor or a blender with the honey and oil, gradually adding enough water to make smooth paste.
4. Take the peppers out of the bag onto a wooden board. Remove the core and seeds, and peel the skin off; it’s a very messy job. Cut the skinned peppers into strips.
5. When the dough has almost doubled in volume, turn it out onto lightly floured surface. Line a large baking sheet with parchment.
6. Divide the dough in half and roll out each half to an oval about 30 x 15cm (11 x 6 in). Spread each with tomato paste, sprinkle with about two thirds of the peppers and fold each slipper lengthwise. Press the edge to seal. Sprinkle the remaining peppers on top, cover loosely with oiled cling film and leave in a warm place for 30 minutes.
7. Preheat the oven to 220C/425F/gas 7. When the slippers have risen and puffed up, take off the cling film, sprinkle with the remaining rosemary and drizzle with olive oil. Bake for 15-20 minutes until golden.
8. Remove from the oven onto a wire rack, sprinkle with sea salt flakes and leave for 5 minutes before cutting. You can reheat the slippers, whole or halves, in a warm oven for about 10 minutes. They will keep for a couple of days in an airtight container or can be frozen. In the latter instance you may underbake them by 5 minutes and bake from frozen for about 15 minutes.