Preheat oven to 350* and line a sheet pan with parchment paper.
Cream together butter, sugar, and molasses until light and fluffy.
Add egg and vanilla, mix until fully incorporated.
In a small bowl, sift together flour, baking powder, and spices.
Add dry ingredients to wet mixture, a little at a time, until combined.
At this point, gently fold in the cranberries, if desired.
Make two logs, about ½ inch thick and four inches wide. Bake at 350* for about 15-18 minutes, or until slightly golden on the edges. (Or, until the log is firm to the touch.)
Allow the logs to cool, then slice on the diagonal, creating roughly 1/2 inch slices.
Turn the slices on their sides, and bake for another 15 – 18 minutes, until crisp.
If using the white chocolate, melt in the microwave or over a double-boiler, and using a pastry bag or parchment cone, pipe a thick line onto one side of the biscotti.