Preheat your oven to 350 degrees F. Line baking sheets with parchment paper.
In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.
Beat in the eggs one at a time, then mix in the vanilla extract.
In a separate medium bowl, whisk together the gluten-free flour blend, baking soda, cinnamon, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Do not overmix.
Stir in the gluten-free rolled oats and raisins by hand until evenly distributed throughout the dough.
Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart. Flatten the tops slightly with the back of a spoon.
Bake for 10 to 12 minutes, or until the edges are lightly golden brown. The centers should still look slightly soft.
Let the cookies cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.
Notes
For the chewiest cookies, use certified gluten-free rolled oats. Standard oats may contain gluten cross-contamination.
If your dough seems too soft, chill it in the refrigerator for 30 minutes before scooping.
If you prefer a softer cookie, slightly reduce the baking time.
If your gluten-free flour blend does not contain xanthan gum, add 1 teaspoon to the dry ingredients.