Spray a 9"x13" Pan with cooking spray AND line it with parchment paper. This doesn't need to be pretty. You can trim up the edges of the bars when you cut them later.
Make The Mixture
In a saucepan on medium heat simmer the corn syrup until it just starts to boil.
During Every step of this recipe use a rubber spatula to continuously stir as it heats. This is to ensure the mixture doesn't burn to the bottom or sides of the pan.
Add in the peanut butter and vanilla. Stir and bring to just to the point that it starts to bubble again.
Add the chocolate and once again heat until it just starts to bubble.
Remove from heat and stir in crushed peanuts.
Immediately pour the mix into your prepared pan.
Let it set up in the fridge for at least 30 minutes before removing from the pan.
turn it upside down so that the top of the bars become the bottom and the smooth bottom is now the top.
Using a sharp knife, cut into 40 even sized bars.
Can be frozen in an airtight bag or container for up to three months and kept in the same packaging on the counter for a week.
Notes
Some people add oatmeal to these bars. I think they are great without the oatmeal though. If you choose to add oatmeal, add it when you add the peanuts and add one cup.