In a large mixing bowl, dissolve yeast and water and let stand for 10 minutes. Add the sugar, egg, salt, flour and butter. Knead the ingredients into wet and sticky dough, about 20 minutes.

Pour a teaspoon of oil in a large bowl and roll the dough in the bowl to evenly coat the dough with oil. Cover the Bowl with a plastic film and set aside in a warm place until the volume doubles, about 1 and half hour.

Line a baking tray with parchment (baking) paper. Gently deflate the dough onto a lightly floured surface and divide into four equal pieces. Shape the pieces into dough balls and using a rolling pin, roll out the dough ball into an oblong disc. Roll the disc onto itself to form a 10-inches long rope. Once you have 4 ropes ready, pinch one end of the ropes together and braid in the following pattern:

Tuck the ends of the braid underneath and place the braid on to the prepared tray. Cover with an oiled plastic sheet and set aside in a warm place until the volume double, about 40-45 minutes.

Preheat the oven to 180°C/350°F. Just before baking, brush the braid with egg wash and sprinkle the sesame seeds, if using. Bake until nicely browned and the bottom of the loaf sounds hollow, about 20-25 minutes.

Remove from the oven and let cool on a wire rack. When completely cooled, slice as desired. Store the bread at room temperature in a paper bag for up to 5 days.