Preparation:
1. Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.
2. In a large bowl, cream together butter, brown sugar, and granulated sugar until light and fluffy.
3. Add egg and vanilla extract, mixing well.

Mixing:
1. In a separate bowl, whisk together flour, baking soda, and salt.
2. Gradually add dry ingredients to the wet mixture, mixing until just combined.
3. Fold in oats, raisins, and chocolate chips.

Baking:
1. Drop rounded tablespoons of dough onto prepared baking sheets.
2. Bake for 10-12 minutes until edges are golden brown.
3. Let cookies cool on baking sheets for a few minutes, then transfer to a wire rack to cool completely.