Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone baking mats to prevent sticking.

In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until the mixture is light and fluffy. This should take about 2-3 minutes using an electric mixer.

Beat in the eggs one at a time, ensuring each egg is fully incorporated before adding the next. Stir in the vanilla extract.

In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon. Gradually add the dry ingredients to the wet mixture, mixing just until combined.

Using a spatula or wooden spoon, fold in the rolled oats and raisins (if using) until evenly distributed throughout the dough.

Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart. Bake in the preheated oven for 10-12 minutes, or until the edges are golden brown and the centers look slightly underbaked.

Allow the cookies to cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely. Enjoy your delicious, chewy oatmeal cookies!