Combine the popcorn and peanuts on a greased rimmed cookie sheet and place it in the preheated oven.
Combine all the remaining ingredients in a saucepan.
Stirring over medium heat, bring the mixture to a boil.
Using a candy or instant read thermometer, bring the mixture to 290 F, or just under the hard-crack stage, the point at which the syrup when dripped into cold water, forms a hard but pliable ball. This will take about 20-25 minutes (or until you notice the mixture turning a slightly darker brown).
Remove the popcorn and peanuts from the oven and working quickly, pour the caramel mixture in a fine stream over them, covering as much as you can and stir to coat.Put the sheet back into the oven. Mix again in five minutes to esure all the popcorn and peanuts are covered.
Let cool, break into pieces and serve.
Store any leftovers in a covered container so it keeps fresh.