Warm a small bowl by rinsing with hot water. Pour in warm water, sprinkle yeast over the top, and allow it to dissolve. Stir in flour, cover with plastic wrap, and let rise for 30 minutes, or until doubled in volume.

In a separate bowl, sprinkle the remaining yeast over warm milk and let it stand until dissolved. In a large bowl, beat together the sugar, eggs, egg yolks, and vanilla. Stir in the milk-yeast mixture, then add the prepared sponge. Mix until combined.

In a large mixing bowl, combine butter with the remaining flour until crumbly. Gradually incorporate the egg mixture. Beat on high speed for 3–4 minutes until the dough appears elastic with visible strands. Stir in candied fruit and citrus zest until evenly distributed.

Transfer the dough into an oiled bowl, cover with plastic wrap, and allow it to rise in a warm place for 2–3 hours, or until doubled in size.

Brush the insides of three 7 x 4-inch paper panettone molds with melted butter. Lightly deflate the dough on a floured surface and divide it into three equal portions. Shape each into a ball and place into the molds. Cover loosely with plastic wrap and let rise again until doubled, about 2 hours.

Preheat the oven to 400°F (200°C). Using oiled kitchen scissors, cut an “X” into the top of each loaf. Combine egg yolk with cream to form an egg wash and brush over the tops.

Place the molds on a baking sheet in the lower third of the oven. Bake for 10 minutes, then reduce oven temperature to 375°F (190°C). Continue baking for an additional 30 minutes, or until a skewer inserted in the center comes out clean. If tops brown too quickly, tent loosely with foil.

Allow loaves to cool completely on a wire rack before slicing.