Navettes, boat-shaped cakes from Provence, are unassertive pastries that benefit from additional flavoring; orange-flower water is traditionally used to make them.
In a small bowl, dissolve yeast in 2 tablespoons lukewarm water. Let stand until creamy, about 10 minutes.
Meanwhile, in another bowl, whisk to gether flour and salt. Place butter and sugar in bowl of electric mixer. Beat, using paddle attachment, until soft and crumbly. Add eggs, dissolved yeast, orange-flower water, and grated zest. Add flour, a cup at a time, and beat on low speeduntil just combined.
Transfer dough to floured work surface, and knead with hands until smooth and no longer sticky. Form into a ball, place in an oiled bowl, cover, and leave to rest in a warm place for 30 minutes.
Rub a large baking sheet with olive oil. Turn the dough out onto lightly floured work surface, and cut into three equal portions. Using your hands, roll each portion into a log about 1-inch thick. Cut each log crosswise into pieces about 2 1/2 inches long. Shape the pieces into tapered boat shapes by rounding and somewhat raising the middle portions, and pinching the ends intopoints. Cover baking sheet with a kitchen towel, and leave in a warm place for 2 hours. Boats will rise somewhat but will not double.
Heat oven to 375 degrees. Using a razor blade or very sharp knife, make a lengthwise slash sown each boat, about 1/3 of its depth. Using a pastry brush, paint the surface of each boat with egg-yolk glaze. Sprinkle with crystal sugar, if desired. Bake until golden, 25 to 30 minutes. Transfer to wire rack to cool.