Whisk together the flours, arrowroot powder, cacao powder, chai spice, baking powder, and salt in a medium bowl until well combined. Set aside.
In a large bowl, beat together the butter and coconut sugar with a hand mixer until pale. Add the egg, vanilla, and milk and beat again until emulsified.
Sift the dry ingredients into the wet ingredients and beat on low speed just until combined. Be careful not to overmix. Fold in the chocolate chips.
Chill the dough in the refrigerator for a minimum of 2 hours to let the spices intensify. Overnight is recommended.
Once the dough has chilled, preheat the oven to 180ºC (350ºF) and line a baking sheet with a silicone mat or non-stick parchment paper.
Divide the batter into 8 equal sized balls. Each one should be about 3 tablespoons of dough. Place the balls evenly spaced apart on the baking sheet and then press each dough ball down slightly to form a thick disc.
Bake the cookies for 8-10 minutes. Be careful not to over-bake them or they will become quite dry. Take them out of the oven when they’re still squidgy in the middle; they will continue to bake on the baking sheet. Leave them to cool on the sheet for 5 minutes and then remove them to a wire rack to finish cooling.