Place a piece of parchment paper onto a rimmed baking sheet and set aside.
In the bowl of an electric mixer, combine together the starter, eggs, vanilla, and brown sugar.
Add in the salt, flour, and spice mix.
Check your dough to see if it needs more flour – you want it to be thick and kind of stiff, but not too dry. It should almost look like cookie dough.
Mix on low speed for 5 minutes.
Add in the butter and mix until incorporated.
Place the dough onto the parchment paper lined baking sheet, forming a log in the middle of the pan.
Cover with plastic wrap and allow to rise for 3-5 hours. It won’t really rise much.
Preheat the oven to 325F.
Bake the log for 35 minutes.
Remove the baking sheet and allow to cool for 5-10 minutes.
Reduce oven temperature to 250F.
Using a bread knife, cut the log into 3/4″ thick slices.
Make sure there is a little bit of room in between each slice, you can kind of separate the slices out from each other a bit, but keep them standing up.
Bake at 250F for 40 minutes.
Remove to a wire rack and allow to cool.
In a microwave safe bowl, break the white chocolate up into pieces.
Melt in the microwave for 30 seconds.
Stir, and continue to melt for 10 second intervals, and stir, until the white chocolate is melted.
Drizzle over the biscotti.
Allow to cool.