Follow the steps in order for the best result.
In a large bowl, cream together the softened butter and brown sugar until the mixture is light and fluffy.
Incorporate the egg and salt into the creamed mixture, stirring until well combined.
Gradually add the dark molasses and buttermilk to the wet ingredients, mixing until evenly blended.
In a separate bowl, sift together the chestnut flour, arrowroot powder, brown rice flour, sorghum flour, baking soda, cinnamon, ginger, clove, allspice, and nutmeg. Sifting is highly recommended to avoid lumps, especially with chestnut flour. Note that the flour ratios can be adjusted to your preference. Brown rice and sorghum flours will result in a slightly less soft cookie, while chestnut flour has a distinct flavor. Experiment to find your ideal texture and taste.
Gradually add approximately 3 cups of the sifted flour mixture to the wet ingredients. Use an electric mixer to combine until smooth.
Incorporate the remaining flour mixture. The dough should become quite stiff, requiring you to stir it in by hand.
Cover the cookie dough tightly and refrigerate overnight to allow the flavors to meld and the dough to firm up.
The next day, preheat your oven to 375°F (190°C).
Lightly flour a clean surface and roll out the chilled dough to a thickness of about 1/4 inch.
Use cookie cutters to cut out desired shapes and transfer them to ungreased baking sheets.
Bake for 8-10 minutes, or until the edges are lightly golden brown. Keep a close eye on them, as baking times may vary depending on your oven.
Remove the cookies from the oven and let them cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.
Enjoy your soft and chewy gluten-free molasses cookies!