Preheat oven to 325º F (165º C). In a large bowl beat together butter, brown sugar, and granulated sugar. Add eggs and vanilla, and beat well. With a large spoon/spatula, mix in flour, baking soda, and sea salt until just barely mixed. Mix in oats, walnuts, and milk chocolate chips. Take heaping spoonfuls (about the size of golfballs) and place on an ungreased baking sheet or parchment-lined baking sheet. Bake for 15 minutes (or 12 minutes for a more gooey cookie) and you don't really want to wait for the cookies to brown. They will be perfectly chewy. Enjoy!