Note: this dough needs to be chilled. Plan ahead!

In a medium bowl, whisk flour, cinnamon, salt, and baking soda. Set aside.

Cream butter and brown sugar in the bowl of a stand mixer fitted with the paddle attachment. Mix until smooth, about 1-2 minutes. Add eggs and vanilla, beat until smooth.

Gradually add dry ingredients into wet, mixing until just combined. Stir in oats and desired mix-ins.

Using a cookie scoop or tablespoon, form dough into 2-tablespoon balls and place on a baking sheet lined with parchment. Cover with plastic wrap and refrigerate for at least 30 minutes.

Preheat oven to 350°F. Place dough balls 2 inches apart on prepared baking sheets.

Bake for 10-12 minutes until the edges are golden. Let cookies cool on the sheet for 10 minutes before transferring to a wire rack.

Store in an airtight container for up to 4 days or freeze for up to 2 months.