Follow these simple steps to create your Oatmeal Raisin Cookie Bars:

1. Preheat Oven: Preheat your oven to 350°F (175°C). Prepare a 9×13-inch baking pan by greasing it or lining it with parchment paper.
2. Cream Butter and Sugars: In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.
3. Add Eggs and Vanilla: Beat in the eggs one at a time, followed by the vanilla extract until well combined.
4. Mix Dry Ingredients: In a separate bowl, whisk together the flour, baking soda, cinnamon, and salt until even.
5. Combine Wet and Dry Ingredients: Gradually add the dry mixture to the wet mixture, stirring until just combined.
6. Fold in Oats and Raisins: Gently fold in the rolled oats, raisins, and nuts (if using) until evenly distributed through the batter.
7. Bake: Spread the batter evenly into the prepared baking pan. Bake in the preheated oven for 25-30 minutes. The edges should be golden brown, and a toothpick inserted in the center should come out clean.

Allow the cookie bars to cool in the pan for 10-15 minutes before slicing them into squares.