In a very large bowl or deep clean dishpan mix the softened butter and sugars together with a hand mixer until well combined.
Mix the peanut butter in and then add the eggs, vanilla, salt and white syrup.
Scrape down the sides of the pan frequently and once everything is mixed well, start adding the oats a little at a time. At this point, you will probably need to abandon the mixer and mix with a spoon.
Once this is all mixed together add in the M&M’s and chocolate chips. Mix with the spoon until the candies and chocolate are distributed evenly.
Use an ice cream scoop or large spoon to dip out ¼ cup or larger mounds of dough. Flatten the dough slightly with your hand if you wish for the cookies to be flatter.
Bake for 12 to 18 minutes. Don’t overbake. The cookies should be just slightly browned around the edges and set in the middle.
Let them cool for a few minutes on the cookie sheet and then remove to parchment or wax paper to cool down completely.