Grease and flour a 9x9-inch baking pan. Preheat the oven to 350 degrees F.
In a large bowl, use an electric mixer to beat together the butter and sugar until creamy. Mix in the molasses, eggs and orange zest.
In a separate bowl, sift together the flour, ginger, cinnamon, cloves, nutmeg and baking soda.
Add 1/2 of the flour mixture to the wet mixture and beat until combined. Mix in 1/2 of the buttermilk. Beat in the remaining flour mixture, then beat in the remaining buttermilk. Scrape the sides and the bottom of the bowl to make sure that all ingredients are incorporated. Stir in the chocolate chips, if using (it's okay to leave them out).
Pour the batter into the prepared pan and bake for 30 minutes or until the top bounces back when you press it gently and the sides are starting to pull away from the edges. Remove the pan from the oven and let cool completely before cutting and serving.