- Preheat the oven to 350°F. Grease and lightly flour a 9" square pan.
- In a large mixing bowl, whisk together the flour, xanthan gum, sugar, baking soda, salt, ginger, cinnamon, cloves, and nutmeg.
- Melt the butter in a heatproof measuring cup. Add the molasses to the cup, and pour into the dry ingredients in the bowl, mixing to moisten.
- Add the water, stirring until everything is moistened. Whisk together the egg and buttermilk. Stir into the batter until it's evenly combined. Stir in the crystallized ginger.
- Pour the batter into the prepared pan, and let it rest on the counter for 15 minutes.
- Bake the cake for 40 to 45 minutes, until it just begins to pull away from the edge of the pan and a toothpick inserted into the center comes out clean.
- Remove the cake from the oven and cool it on a rack for 15 minutes before slicing; gingerbread is best served warm with whipped cream or ice cream.