Step 1: Preheat your oven to 350°F (175°C).
Step 2: Cream the butter and sugars together in a large mixing bowl until light and fluffy.
Step 3: Add the egg and vanilla extract, mixing well until fully incorporated.
Step 4: In a separate bowl, whisk together the flour, baking soda, cinnamon, and salt. Gradually add this to the wet ingredients, stirring until just combined.
Step 5: Fold in the oats, chocolate chips, and optional raisins or nuts.
Step 6: Scoop rounded balls of dough onto a lined baking sheet, leaving space between each.
Step 7: Bake for 10-12 minutes or until edges are golden brown.
Step 8: Cool on the baking sheet for 5 minutes before transferring to a wire rack.