In a large bowl, combine flour, sugar, yeast, and salt.

Add water and eggs and beat for about 5 minutes.

Place the dough in a buttered bowl.

Allow it to rise in a warm place until doubled in size, about 2 hours.

Deflate the risen starter.

Break it into pieces and place in a mixing bowl.

Mix in sugar, butter, and orange zest.

Beat in the flour and egg yolks.

Slowly mix in the water until the dough is slightly sticky but smooth. Add additional water or flour if needed.

Lightly knead the dough on a floured work surface.

Form it into a round dome.

Butter and flour a mixing bowl and place the dough in it, cover.

Let sit in a warm place until it has doubled in size, about 2 hours.

Punch down the risen dough.

Set aside one-quarter of the dough.

Mound the remaining dough on a floured work surface.

Press fist-size balls of dough into 6-inch rounds.

Cover and let rise for 1 hour.

Divide the reserved dough into equal parts based on the number of dough rounds.

Shape each part into two bone-shaped logs, each roughly 7 inches long, pinching in the center.

Set on a baking sheet and let rise until the cakes are done rising.

Set two bones on top of each round, intersecting in the middle to form a crossbones.

Brush the cakes with the beaten egg yolks.

Preheat the oven to 325°F.

Butter two baking sheets.

Transfer the cakes to the sheets and bake for 15 to 20 minutes, until golden and springy.

Open the oven door and let sit for 5 minutes.

Remove the cakes from the oven.

Brush the surface of each one with melted butter.

Sprinkle with sugar.

Let cool before serving.