Preheat oven to 375. Grease two baking sheets.
Cream butter and sugar in the bowl of a stand-mixer. Incorporate eggs, one at a time, followed by molasses.
Sift together dry ingredients, spices, and orange zest. Gradually add dry ingredients to wet ingredients and mix until well-combined and a stiff dough forms. Add more flour by the tablespoon if dough is sticky.
Divide dough in half.
Take one portion of dough and shape it into a roll, about 10-12 inches long. Pat the roll into a rectangle, about 3/4 inch thick on baking sheet, and as wide as you'd like your cookies (I did mine about 5-6 inches) . Make the rectangle as uniform in thickness as possible for even baking. Repeat with other half of dough.
Bake for 25 minutes. Remove pans from oven and reduce baking temp to 300. Cool cookies about 5 minutes or until cool enough to touch.
With a long, sharp, straight-edged knife, slice the rectangles into 3/4 inch wide cookie strips, discarding the rough edge on each end. Space cookies out on baking sheets and place them back in the oven. Bake another 8-10 minutes. Cookies will firm up and dry out as they cool.
Melt the white chocolate and shortening in a shallow dish (wide enough for biscotti to be dipped) in the microwave, stirring every 30 seconds until smooth. Dip the bottom of each cookie into the chocolate and lay cookies on their side on waxed paper until set.
Store in airtight containers or bags.