- Make the sponge: In the bowl of a stand mixer, stir together water, flour, yeast, and salt. Cover; let mixture sit in a warm place for at least 30 minutes and up to 2 hours. The surface should look bubbly and like a sponge. 
- Fit stand mixer with a dough hook attachment. With mixer on low speed, add sugar, oil, vanilla extract, eggs and yolks. 
- Add remaining flour, 1/2 cup at a time and knead until the dough is smooth and tacky, but not too wet or sticky. 
- Cover and allow dough to rest for 1 hour in a warm place, or until it doubles in size. Alternatively, you can cover and allow it to slowly rise in the refrigerator overnight. 
- Assemble Kokosh: Line 2 baking sheets with parchment paper. (You can fit two kokosh cakes lengthwise onto one tray, just keep them a few inches apart.) 
- Once dough doubles in size, punch down and divide into three equal pieces. (If refrigerated overnight, allow dough to come to room temperature before proceeding.) 
- Preheat oven to 350°F. 
- Roll each piece into approximately a 10x14-inch rectangle. Spread 1/3 cup of chocolate spread over each dough. 
- Make filling: Combine sugar, cocoa, salt and coffee (optional) in a small bowl. Sprinkle 1/2 to 2/3 cup over each dough. 
- Roll each piece into a log, starting from the shorter side and pinch edges to seal. Use a rolling pin to slightly flatten the kokosh cake. Place on prepared baking sheets. 
- Brush with egg wash and bake for 20-25 minutes, until light golden brown.