Mix half the flour, half the yeast, and 475ml lukewarm water in a bowl to form a batter.
Rest batter in a warm room for 30 minutes until bubbling.
Add remaining flour, yeast, salt, and oil to the starter and mix well.
Knead the dough on an oiled surface for 10 minutes until elastic.
Place dough in an oiled bowl, cover, and let rise for 1 hour until doubled.
Fry onion in olive oil until browned, then mix in tomato purée, harissa, saffron, and 4 tbsp water.
Divide the proved dough into four equal portions on a floured surface.
Roll each portion into a 10x50cm rectangle about 5mm thick.
Spread the cooling filling over dough leaving a 2cm border and top with olives and cheese.
Roll dough tightly lengthways into 50cm sausages and pinch the seams shut.
Stretch the rolls carefully until they are 80cm long.
Plait the four strands together on a floured surface.
Form the plait into a ring around a greased 15cm metal ring on a floured baking tray.
Cover and prove the ring for 45 minutes until increased in size.
Blend dip ingredients with 4 tbsp water in a food processor until smooth.
Preheat oven to 220°C.
Brush bread with egg wash and bake for 20 minutes.
Reduce oven to 200°C and bake for another 25 minutes.
Cool bread on a wire rack and warm the dip in a saucepan.
Serve bread with hot dip in the center and a garnish of chopped mint.