First make the sauce. In a good size saucepan or cast-iron casserole, gently cook the onion, garlic, pimenton, cumin and saffron in the oil for about 5 minutes until soft. Add the tomatoes and stock, bring to the boil, season with salt and pepper and simmer for 30 minutes.
Meanwhile, combine all the ingredients for the meatballs in a bowl, season with salt and freshly ground black pepper and mix well. Mould into balls about the size of a 10p and leave to rest in the fridge for 30 minutes.
Heat some vegetable oil in a heavy bottomed frying pan until almost smoking and fry the meatballs a few at a time until nicely coloured, then drain in a colander or on some kitchen paper. Add the meatballs to the sauce and simmer for 10 minutes.
Preheat the oven to 200°C/390°F/ Gas mark 6.
To serve, arrange the meatballs and sauce round the edge of a tagine, ovenproof dish or individual tagines or serving dishes, leaving a gap in the middle of each individual dish, or four gaps in the larger ones. Crack an egg into the gaps, cover the dishes with foil or the tagine lid if your oven is big enough and put them in the oven for about 5-10 minutes until the white is just set. Alternatively simmer in the tagine over the stove with the lid on for 5-7 minutes or until your egg white has cooked.
Serve immediately with the tagine lids on. Offer bread or couscous to mop up the yolk and sauce.