Here’s a trick I learned when making sweet dough that has a large fat content (in this case, a lot of oil). Oil will keep the dough from rising, so make a sponge first to get a better rise: dissolve the yeast in a bowl of warm water. Add half the flour to the mix and mix well. Cover well with plastic wrap, and then let it rise until it doubles in size.
Meanwhile, mix the oil and sugar well. Add the eggs and vanilla.
When the sponge (the flour-yeast mix) doubles in size, add it to the rest of the dough. Add the rest of the flour and the salt.
Mix well in a standing mixer with a dough hook; you can add some more flour if the dough is too sticky.
Mix for about 8 minutes after the dough comes all together, then put it onto a floured sheet pan. Cover well with plastic wrap and leave in the fridge until it is cool, around one hour.
Cut dough in half and roll out (it should roll nicely, the fridge makes it easy to work with). Roll out into a long, wide rectangle.
Pour liquid marble all over the surface (should take around a whole container of store-bought marble to fill the cake). Roll it up jelly roll style.
Make long deep slices on the top so the inside can bake. Brush with egg wash for a nice shine.
Bake for at least 40 minutes, until nice and golden and you are sure it is well baked inside.
When it comes out of the oven, pull it out and use a flat pan to press the kokosh cake down, to make the cake nice and gooey.
You can brush egg white and sugar on top of the hot cake so it will be left with a nice sticky shine on the top.
Liquid marble can be found in most kosher stores.