Preheat oven to 350 F. Line 2 sheet pans with silicone baking mats or parchment paper; set aside.
In a large bowl, beat together butter and sugar until well-combined, about 2-3 minutes.
Beat in eggs and vanilla, scraping the sides of the bowl as needed.
Add oats, flour, baking soda, and salt; stir until just combined.
Stir in cranberries and chocolate chips, if using.
Using a medium cookie scoop (1 ½-tablespoons), drop dough about 2 inches apart on prepared baking sheet.
Bake for about 9-12 minutes, or until light golden brown.
Let cool on baking sheet.
Notes
Butter: The butter should be at cool room temperature. It should dent slightly when pressed but otherwise hold its shape. If the butter is too warm and smooshy, then the cookies will spread too much at they bake.
Brown sugar: I use light brown sugar, but you can use dark brown sugar if you want more of a toffee note to your cookies.
Oats: This cookie recipe uses old-fashioned oats, not quick oats.
Baking: Oven temps can vary, so adjust your baking times accordingly. The cookies should be light brown at the edges and look slightly underdone in the center for soft cookies. If you want crispier cookies, add an additional 1-2 minutes to the baking time.