Step 1Heat the oven to 350 degrees.
Step 2In the bowl of a standing mixer, mix the butter and sugars on medium speed until very well combined, about 1 minute. Add the eggs, one at a time, and the vanilla and mix until combined.
Step 3Add the flour, salt and baking soda directly into the bowl and mix on medium speed until well combined, about a minute. Scrape the sides of the bowl and make sure that the dough on the bottom is mixed too. Add the oats and the chocolate and mix it up briefly, until combined. At this point, you can refrigerate the dough or bake the cookies immediately.
Step 4Line trays with parchment paper and spoon out big balls of dough, about one-quarter cup, onto the parchment. Using your fingers, squash the balls down a little. Because these are big cookies and they'll spread during backing, put 6 balls of dough on each tray.
Step 5Bake the cookies until they just start to brown around the edges, rotating the trays halfway so they bake evenly, about 15 minutes. Remove the cookies to a rack to cool. Repeat with all of the cookie dough. If you don't want to bake them right away, or have time to bake only some of them, the dough will keep, well-wrapped, for a few days in the refrigerator. Once baked, the cookies will keep for up to 4 days in an airtight container or for up to a month frozen.