Pre-heat your oven to 350°. Line a baking sheet with parchment paper and set aside.
In a large bowl, beat the butter, sugar, and orange zest together with an electric mixer until light adn fluffy. Add in the eggs 1 at a time. Mix in the vanilla.
In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add this to your butter mixture. Mix in the dried cranberries. The dough should be thick.
With lightly floured hands, divide the dough in half and place on the baking sheet. Shape the dough into two separate logs, about 10-12" long and 2-3" wide. Make sure to place your logs about 3-4" apart because they do spread as they bake. The dough will seem sticky, so just lightly dust it with flour and keep your hands floured while shaping the logs.
Bake for 30 minutes at 350° or until golden brown. Take the biscotti out of the oven and allow it to cool completely, about 45 minutes or so.
Once cooled, cut the loaves on a diagonal into slices that are about 1-1½ inches thick. I used a large chef's knife but you could also use a bread knife. Place the biscotti cut side down on the parchment paper-lined baking sheet.
Return to the oven at 350° and bake for 10 minutes. Then flip each biscotti oven gently and return to the oven for another 10 minutes. They should be lightly golden brown when done baking. Allow them to cool completely.
Optional but recommended: Melt white chocolate in 20-second increments (stirring in between) until melted and use a spoon to drizzle over cooled biscotti. Allow white chocolate to harden before serving.