Preheat your oven to 325 degrees and prepare the baking sheets by lining them with either parchment paper or a silicone mat.
In a medium mixing bowl, add the flour, baking soda, salt, and cinnamon, whisk to combine, and then set this mixture aside.
Add the butter to a microwave-safe bowl and heat in 30-second intervals until the butter is melted.
In the bowl of your stand mixer add the the melted butter, brown sugar, and white sugar. Use the whisk attachment and whip them together until you achieve a light and fluffy texture, which typically takes around 2-3 minutes.
Next, change the stand mixer attachment to the paddle attachment and add the eggs one egg at a time into the mixture and mix until combined.
Gradually add the flour mixture and oats into the bowl, stirring just until everything is evenly combined.
Stir in the cranberries. If adding nuts or chocolate chips add them in now.
Using a cookie scoop or spoon, scoop balls of the cookie dough onto the prepared cookie sheet.
Bake in the oven for 14-16 minutes, until the cookies are a light golden brown.
Once the cookies are done baking, allow them to rest on the cookie sheet for about 5 minutes before gently transferring them to a wire rack until completely cooled.