Using a double boiler or microwave, melt the butter and chocolate chips together and pour into a medium sized bowl. Allow to cool slightly (5-8 minutes).
In a stand mixer, cream together sugar and eggs.
Add in melted chocolate, cocoa powder, sourdough starter, salt, and vanilla. Mix to combine.
Slowly add in your flour 1/2 cup at a time until well incorporated.
Form into short loaves on greased or parchment lined cookie sheet.
Let rise for 2 hours.
Preheat oven to 350°F.
Bake the loaves for 30 minutes.
Remove from the oven and cut the loaves diagonally to create the biscotti shapes and lay on their sides on the baking sheet.
Decrease oven temperature to 200°F.
Bake at 200°F for about an hour until desired crunchiness is reached, flipping the biscotti half way through to its other side.
Let cool.