Pre-heat the oven to 350 and line two sheet trays with silicone mats. Whisk the tahini, mashed sweet potato, maple syrup, cinnamon, pumpkin spice, nutmeg and vanilla together in a large mixing bowl. It will stick to the whisk a bit so use a spoon to scrape it back off. Then switch to a spatula and fold in the flour and baking powder until it disappears and you have a dough. It will be slightly crumbly, so use your clean hands to bring it together into a soft, smooth ball of dough. 

Use a 1.5 inch cookie scoop to scoop perfect little mounds of the dough onto the lined sheets, with 12 on each sheet. Press each one down with a fork both vertically and horizontally to flatten them out and make interesting cross marks. Bake them for about 10 minutes, until golden and slightly crisp around the edges. Let them cool, then store them in an airtight container to enjoy as you want them! They'll keep for days.