Prepare the brown butter in advance:  In a medium saucepan or skillet, melt butter until foamy and continue to cook, watching carefully, until the solids begin to turn brown and butter begins to smell nutty. Remove from heat, pour into a heat-safe bowl, and place in fridge to re-solidify. This can take a few hours, so feel free to prepare the day before. Prior to baking, remove butter from fridge and allow to soften slightly. 

When you’re ready to bake, preheat oven to 350 degrees. Line two baking sheets with parchment paper.

In a medium bowl, whisk together flour, baking soda, salt, and spices. 

In a separate bowl or the bowl of a stand mixer, cream the butter and sugars together until light and fluffy (how long this takes depends on the consistency of your butter; softer butter takes less time). Beat in the eggs one at a time, then stir in the vanilla. 

Add the flour mixture and beat on low just until combined. Add oats. When those are incorporated, stir in nuts and/or add-ins, if using. 

Using a cookie scoop or large spoon, drop dough on prepared baking sheets. For standard two-inch cookies, use a medium scoop. For large bakery-size cookies use quarter-cup dollops. This is a sturdy dough that doesn’t spread much, so for aesthetically pleasing, uniform cookies, flatten the tops of the dough mounds slightly. Leave about one inch in between cookies. 

Bake at 350 degrees for 12-15 minutes, until edges are just beginning to brown and centers look slightly undone. Cool slightly on the pan, then transfer to a baking rack to cool fully.  Store in an airtight container.