Preheat oven to 350ºF. Prepare baking sheets by lining them with parchment paper or nonstick baking mats.
In a large bowl, using a hand mixer or stand mixer with the paddle attachment, cream together the butter, sugars, eggs, and vanilla until smooth.
Stir together the flour, baking soda, and salt in a separate small or medium bowl.
Add the flour mixture to the wet ingredients and mix until combined, scraping the sides of the bowl as needed.
Mix in the oats until combined.
Mix in the chocolate chips, chopped chocolate and walnuts.
Using a cookie scoop, drop cookie dough balls onto prepared cookie sheets. Flatten slightly with the bottom of a glass if you'd like the cookies to be flatter.
Sprinkle the tops with coarse sugar if desired, or press a few chocolate chips into the top of the cookies before baking. This makes them extra pretty.
Bake 10 minutes. Don't overbake.
Let them cool for 2-3 minutes on the cookie sheets before them to a wire rack to cool completely.
Store in an airtight container at room temperature for up to 5 days. Freeze cookies for up to 8 weeks.
Notes
If you don't have a kitchen scale, measure the flour carefully so you don't end up with too much flour in the cookies, which would make them dry. Carefully spoon the flour into the measuring cup, then level it off with a knife. Don't pack the flour in the cups.Refer to the article above for more tips and tricks.The calories shown are based on the recipe making 36 cookies, with 1 serving being 1 cookie. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information. The information in the nutrition box are calculated through a program and there is room for error. If you need an accurate count, I recommend running the ingredients through your favorite nutrition calculator.**