Preheat the oven to 375F and adjust racks to upper and lower thirds. Line two baking sheets with parchment.
In a stand mixer or large bowl, cream the butter and sugars on medium until light and fluffy. At least 3 minutes.
Add the eggs one at a time and incorporate fully.
Add the vanilla and combine.
In a separate medium bowl, whisk together the dry ingredients (except the oats and add-ins, if using).
Add the dry ingredients to the butter mixture and mix on low until just incorporated.
Add the oats and add-ins and mix on low again.
Portion the cookies onto the sheets. Leave at least an inch or two for spreading.
Bake, rotating the sheets halfway through.
Transfer cookies to wire racks to cool completely