To the bowl of a stand mixer fitted with the paddle attachment (or a large mixing bowl and electric mixer), combine the egg, butter, sugars, vanilla. Beat on medium-high speed until creamed and well combined, about 4 minutes.

Stop, scrape down the sides of the bowl, and add the oats, flour, cinnamon, baking soda, optional salt. Beat on low speed until just combined, about 1 minute.

Stop, scrape down the sides of the bowl, and add the chocolate chips, optional raisins or nuts. Beat on low speed until just combined, about 30 seconds.

Using a large cookie scoop, 1/4-cup measure, or your hands, form approximately 12 equal-sized mounds of dough, roll into balls, and flatten slightly. Place a few chocolate chips on top of each mound.

Place mounds on a large plate or tray, cover with plastic wrap, and refrigerate for at least 2 hours.

Preheat oven to 350F. Line a baking sheet with a silicone mat or spray with cooking spray. Place dough mounds on the baking sheet, spacing at least 2 inches apart.

Bake for about 11 minutes, or until edges have set and tops are just set. Cookies will firm up as they cool.

Allow cookies to cool on the baking sheet for about 10 minutes before transferring to a wire rack to cool completely.