Using your handheld or stand mixer cream the butter, sugar, egg, and vanilla together, on medium speed, until smooth. Scrape down the sides and bottom of the bowl as needed.
Slowly add the flour, oats, baking soda, cinnamon, and salt together and mix on low until blended.
Add any combination of raisins, chocolate chips, toffee bits and nuts. Stir with a spoon or on low speed.
Dough will be thick. Chill dough for at least 60 minutes in the refrigerator to help reduce spreading.
Preheat your oven to 350 degrees. Prepare your rimmed baking sheets with cooking spray. Set aside.
Form discs of dough about 2 inches wide and ¾-1 inch high.
Bake for 20-25 minutes until very lightly browned on the edges. The centers will look uncooked and shiny.
Remove from the oven and let cool on your baking sheet for at least 5 minutes before transferring to a wire rack. Enjoy!