Preheat the oven to 350 degrees.
This makes a lot of dough, so I use my Kitchen Aid stand mixer and paddle attachment. It handles all the ingredients really well. You can also use a large mixing bowl and electric mixer, but definitely stir in all the add-ins and use a large enough bowl to hold everything.
Cream the butter and shortening, then add both sugars, the eggs, salt, and vanilla. Beat at medium speed until well combined. Combine flour, baking powder, and baking soda in a separate bowl, then add into the butter mixture and mix well.
Stir in the oats, nuts, chocolate chips, coconut, Corn Flakes, and/or any other add-ins you like. Butterscotch chips, raisins, Craisins, sliced almonds, Rice Krispies cereal, pretzels...whatever you have on hand and love!
Use a 1/4 measuring cup to scoop out the cookie dough, and place on a baking sheet lined with parchment paper or a silicone baking mat. You could also use a large cookie scoop or ice cream scoop about the same size. For smaller cookies, use a cookie scoop to form your cookies, then alter the baking time by a few minutes.
Place cookie sheets in the oven, and bake 10-12 minutes, or slightly longer for a crispier cookie. Let sit on the cookie sheet for a few minutes before moving to cool completely on wire racks. Store in airtight containers for 3-5 days on the counter, and about a week in the refrigerator.