Cream together unsalted butter and sugars, until light and fluffy. ***Tip*** If you don't have room temperature butter then I just use my microwave set at 10% power a minute per side of butter for a total of 4-6 minutes, just be careful not to end up with melted butter, which I have done a couple of times because I somehow missed changing the power.
Add eggs 1 at a time, I prefer putting eggs in hot tap water for 4-5 minutes so they mix better. Beat well after each addition. Beat in vanilla extract.
Stir in cornflakes and oats to this mixture
Sift together, flour, baking soda, baking powder, salt. I prefer to make sure they are all well mixed by adding 1 cup of flour to sifter, then 1/2 teaspoon of the salt, baking soda and baking powder, then alternate this for the other 3 cups of flour.
Gradually stir in the sifted ingredients to the creamed mixture.
Add toasted pecans and chocolate chips and distribute throughout dough. To toast pecans, spread a single layer on sheet tray and bake at 350 degrees for 8 minutes. Be very careful not to burn them.
Place oven rack at the top of oven and preheat to 325 degrees.
Drop by standard sized ice cream scoop onto greased cookie sheet. These cookies are large so only 6 to a standard sized cookie sheet. My sheets are 19x15 so 8 will fit.
Bake at 325 degrees for 16-18 minutes, depending on your oven.