In a large bowl, cream the butter and sugars until light and fluffy, about 3 minutes. In a medium bow, whisk together the oat flour, baking soda, cinnamon, and salt.
Beat in the eggs until incorporated, then beat in the flour mix. Stir in the oats and raisins.
Preheat the oven to 350℉ and line a 13x9-inch pan with parchment paper. Place the dough in the pan, using a rubber spatula to spread it out evenly, then smooth the top. Rest the batter while the oven heats.
Bake the bars for about 35 minutes, until they are set and lightly browned. Remove the pan from the oven and cool completely on a wire rack.
When the bars have cooled, use a sharp knife to cut them into squares. Store in an airtight container for up to 5 days.
Notes
If you can't eat oats: You can try quinoa flakes and a different gluten-free flour such as brown rice flour for the oats and oat flour.
Rest the batter: Always rest the batter while the oven heats so that the flour can hydrate, leading to better bars.
Brown the butter: For more depth of flavor, try browning the butter or just melting it rather than softening it. Then whisk or beat in the sugars and proceed with the recipe.
Don't overbake: The key to the best cookie bars (and cookies) is to not overbake them! Check the bars and when they are lightly browned and set, pull them from the oven so that they don't turn out too dry.