Add the yeast into a small bowl with 2 teaspoons of water and mix together, let it stand for 10 minutes.
In a mixing bowl with the hook attachment, add the flour, yeast mixture, honey, sugar, vanilla extract, whole eggs, egg yolk, salt, and mix on slow speed for 2 minutes.
Add the pre-dough and continue to mix for 3 minutes.
Increase the speed to setting 3 and mix for 2 minutes then gradually add the butter and continue to mix for about 15 minutes.
Add in the orange and lemon zest and mix on high speed for 2 additional minutes or until the dough is fully developed. The dough should be smooth and stretchy with good elastic properties. You can do the windowpane test to ensure the dough is developed.
Remove the dough and shape into a round boule.
Coat a Pandoro pan with butter and place the shaped dough ball into the Pandoro pan with the seam facing outward.
Cover the baking pan and let it rise for about 2 hours or until the dough reaches the top of the pan.
Preheat the oven to 160°C (320°F) and bake for about 30-35 minutes or until the internal temperature of the cake reaches 96°C.
Remove the oven and cool for 20 minutes before removing it from the pan.
Garnish with icing sugar and serve.