Preheat oven to 375 degrees. Line two baking sheets with parchment paper.
Using a stand mixer, cream together butter and sugar (both kinds) until light and fluffy.
Mix eggs and vanilla into butter mixture.
In a medium bowl, whisk together flour, cinnamon, baking soda, and salt.
Transfer flour mixture to butter mixture, then mix until well combined.
Add rolled oats, chocolate, and nuts to dough, then mix well.
Drop heaping tablespoons of the dough onto the lined cookie sheets, spacing at least 2 inches apart.
Bake cookies until golden brown on edges and bottom, about 13 to 15 minutes. (Bake the cookies in batches, one pan at a time.)
Let cookies cool on pan for 5 minutes, then transfer to a cooling rack.
Store cookies in an airtight container. Enjoy!
Notes
This recipe makes about 28 to 30 large cookies, depending on how generously you size them. To measure flour, lightly spoon it into a dry measuring cup, then use a knife (or something else with a straight edge) to level off the top. Do not scoop the measuring cup into the flour ... you'll end up packing the flour, and the cookies will turn out dry.When measuring the chocolate and nuts, I recommend being generous and using a heaping (rounded) ½ cup of each. You could also add more, or do all chocolate or all nuts. Just keep in mind that the dough is very thick, so don't go too crazy or it will be hard to mix.If you have one, a stand mixer will work best for this recipe, because the dough is very thick. As you mix the cookies, make sure to stop occasionally to scrape down the mixer's bowl and paddle with a spatula.Make sure to read the info before this recipe card for more tips, step-by-step photos, variations, and related recipes!