Measure out all ingredients and arrange them within reach—this is essential for smooth baking. In a small bowl, whisk together the oat flour, tapioca starch, baking powder, cinnamon, nutmeg, and sea salt. Set this dry mixture aside. I prefer using freshly ground cinnamon here because it releases so much more aromatic flavor than pre-ground spice. Ensure your butter is truly softened to room temperature and your egg is also at room temperature; this helps everything incorporate evenly and creates a lighter, more tender cookie.

In a large mixing bowl, combine the softened butter, brown sugar, and cane sugar. Using an electric mixer or vigorous hand-mixing, cream these together for 2-3 minutes until the mixture is light, fluffy, and pale in color. This creaming process incorporates air into the dough, which helps the cookies rise slightly and become tender rather than dense. Stop occasionally to scrape down the bowl to ensure everything is evenly combined.

Add the room-temperature egg to the creamed butter-sugar mixture and beat until fully incorporated, about 1 minute. Pour in the vanilla extract and mix to combine. Then add the dry spice ingredients (cinnamon, nutmeg, salt) directly to the wet mixture and stir until you no longer see streaks of spice. I like to add the spices to the wet mixture at this point rather than waiting—it helps them distribute more evenly throughout the dough and prevents any clumping.

Gently fold the dry ingredient mixture from Step 1 into the wet mixture from Step 3 using a spatula or wooden spoon. Mix until just combined—you want to avoid overmixing, which can develop gluten and make the cookies tough. The dough should come together without any visible flour streaks. Cover the bowl with plastic wrap and let the dough rest at room temperature for 30 minutes. This resting period allows the oat flour to fully hydrate and helps the flavors meld together, which results in better-textured cookies.

While the dough rests, preheat your oven to 350°F and line your baking sheets with parchment paper. After the 30-minute rest, remove the dough from the bowl and fold in the rolled oats and raisins using a spatula. Stir gently until the oats and raisins are evenly distributed throughout the dough. I like to use fresh, plump raisins because they stay moist during baking and provide better texture and sweetness than hard, old raisins.

Using a cookie scoop or spoon, drop rounded portions of dough onto the prepared baking sheets, spacing them about 2 inches apart. Gently flatten each cookie with the bottom of a measuring cup or your palm to about 1/2-inch thickness. Bake for 10-12 minutes until the edges are light golden brown but the centers still look slightly underdone—they will continue to cook as they cool. The cookies should feel just set on the outside but still have a tiny bit of give in the center for a chewy interior.

Remove the cookies from the oven and let them cool on the baking sheet for 5 minutes—this allows them to set without becoming too firm. Transfer the cookies to a wire cooling rack to cool completely. This two-stage cooling process prevents the cookies from being too delicate to move while still ensuring they finish cooking evenly. Store cooled cookies in an airtight container for up to 5 days.