Preheat oven to 350 °F (175 °C) and grease a 9×9‑inch baking pan; line with parchment paper for easy lifting.

In a medium bowl, whisk together flour, baking soda, cinnamon, and salt.

In a large bowl, beat the butter and brown sugar until light and fluffy (about 2–3 minutes).

Add eggs one at a time, then mix in vanilla extract.

Gradually add the dry ingredients to the wet mixture until just combined.

Fold in the oats and raisins until evenly distributed.

Spread the dough evenly into the prepared pan and bake for 18–20 minutes or until the edges turn golden.

Let the bars cool completely in the pan.

To prepare the frosting, beat butter until smooth.

Gradually add powdered sugar, then blend in maple syrup, heavy cream, cinnamon, and optional maple extract until creamy and spreadable.

Spread the frosting over the cooled bars, then slice into squares and serve.