Creating Oatmeal Raisin Cookie Bars is simple if you follow these easy steps:

1. Preheat Oven: Preheat your oven to 350°F (175°C). Line a 9×13-inch baking dish with parchment paper, allowing some overhang for easy removal later.

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, mixing well until combined.

4. Combine Dry Ingredients: In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon (if using).

5. Mix Ingredients: Gradually add the dry ingredient mixture to the wet ingredients, stirring until just combined.

6. Add Oats and Raisins: Fold in the rolled oats and raisins until evenly distributed throughout the batter.

7. Spread Batter: Pour the batter into the prepared baking dish and spread it evenly, pressing it down gently.

8. Bake: Place the baking dish in the preheated oven and bake for 25-30 minutes, or until the edges are golden brown and a toothpick inserted in the center comes out clean.

9. Cool: Remove from the oven and let the bars cool in the baking dish for about 10-15 minutes, then lift them out using the parchment paper and allow them to cool completely on a wire rack.

10. Slice: Once cooled, use a sharp knife to cut the bars into squares or rectangles.