Preheat oven to 350 degrees F (180 degrees C). Line 2 baking sheets with parchment paper.
Add the melted butter, brown sugar, and caster sugar to a large mixing bowl. Beat with a wooden spoon to combine.
Add the pumpkin puree, flax egg, and vanilla extract. Mix well.
In another mixing bowl, whisk together flour, salt, xanthan gum, baking soda, cinnamon, nutmeg, and ginger.
Sieve the flour mixture into the wet ingredients. Mix together gently.
Fold in chocolate chips.
Chill the dough in the refrigerator for 1 hour to make it easier to handle. You can also put it in the freezer for 20 to 30 minutes.
Roll the dough into balls. Place them on lined baking sheets.
Bake for 14 to 16 minutes, until golden brown on top. Leave the cookies on the baking sheets for 5 to 10 minutes before moving them to a wire rack with a spatula.