To make the levain:

1. Weigh the flour; or measure it by gently spooning it into a cup, then sweeping off any excess. Combine the flour, sourdough starter, and water in a medium-sized mixing bowl. The mixture should feel like dough, tacky and slightly sticky. Stir in more flour or water as needed. Cover, and allow the levain to rest at room temperature for 6 to 8 hours, or more, until it doubles in size or increases significantly.

Soak the dried fruits to soften them.

1. In a small glass bowl, add the golden raisins and dried cranberries. Pour boiling water over the fruit and allow it to soak for at least 20 minutes. Drain completely before incorporating into the dough. This is optional, but recommended. Note: If you soak the dried fruit, you’ll probably need to add a little more flour to the final dough.

To make the dough:

1. Cut the levain into 10-12 pieces and place in the bowl of a stand mixer. In liquid measuring cup, stir the lukewarm water and instant yeast until dissolved. Let the water/yeast mixture rest for 1 minute, then pour over the levain to soften the pieces.
2. In a separate bowl, whisk the eggs and vanilla together, and pour over the starter mixture. Stir until combined.
3. Add the flour and salt. Using the paddle attachment, mix on low speed for 2 minutes. The dough will be more like batter than dough at this point, but it should hold together. Scrap down the sides of the bowl using a wet dough scraper or spatula.
4. Continue mixing on low speed while adding the sugar ½ tablespoon at a time. Incorporate thoroughly before adding the next addition. The dough will be smoother, but still sticky. To develop the gluten, increase the mixer speed to medium and mix for about 5 minutes, scraping down the bowl and paddle as needed.
5. Switch to the dough hook, and add the butter gradually, 1 tablespoon at a time, while mixing on medium-low speed. Wait until each piece is incorporated before adding the next tablespoon of butter. Scrap down the sides of the bowl and the dough hook as needed. Increase the speed to medium-high, if desired. After about 5 minutes, the dough should be shiny, soft, and sticky when pressed between your fingers.
6. Scrap down the bowl, and mix again on medium speed for about 5 minutes to develop the gluten fully. When the dough is ready, you should be able to pull out long strands of dough.
7. Place the dough in a large bowl, cover, and allow to rise, covered, for 1 to 1 1/2 hours, or until it’s puffy (though not necessarily doubled in bulk) before mixing in the fruit and zest.
8. Gently deflate the dough, and knead in the fruits and zest.
9. For mini panettones, divide the dough into 3 ounces/85-gram pieces or use enough dough to fill the baking mold 1/3 full. Shape the pieces into a ball and place in the panettone baking papers or a muffin tin. Place the baking papers on a baking sheet or in a rectangular baking pan.
10. Cover the pan and let the dough rise until it’s just crested over the rim of the pan or papers, this could take several hours, depending on how much dried yeast you add to the final dough.
11. Preheat the oven to 350°F about 15 minutes before you plan to bake.
12. Bake the mini panettones for 25-30 minutes, check after the first 10 minutes and rotate the pan for even baking. Continue baking until the panettones are golden brown on all sides and sound hollow when tapped. The internal temperature should be 185°F (85°C) in the center when using a digital thermometer.
13. Remove the panettones from the oven and cool completely. No need to remove the papers for the smaller panettones.
14. Store at room temperature, well-wrapped, for up to a week; freeze for longer storage.