For each dough, dissolve the yeast in warm liquid, add the salt and sugar, and stir. Sift in the flour and pour in the olive oil.
Knead both doughs - white and black. Cover the bowls with plastic wrap and leave in a warm place for one hour.
This is how the dough should rise.
Turn the dough out onto a floured surface and roll each piece into a rectangular sheet. Stack one on top of the other, brushing each layer with melted butter.
Roll up into a tight log, pinch the seam well, and roll the ends smooth. Transfer to a baking tray, score the top, and let proof for 30-40 minutes, then brush with beaten egg.
Bake the loaf in an oven preheated to 200°C for 30 minutes, with a tray of boiling water on the bottom rack for steam.
Let the finished loaf cool completely. Enjoy!