Preheat your oven to 350°F (175°C). Line 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 light and fluffy. This should take about 2-3 minutes using an electric mixer.

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

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

Using a spatula, fold in the rolled oats and raisins or chocolate chips (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 warm or store in an airtight container for up to a week.