Begin by popping your popcorn. You can use whichever method you prefer: air popped, on the stove top or in the microwave. If you buy microwave popcorn, I would recommend getting plain popcorn. When your popcorn is popped, remove all the unpopped kernels so that no one breaks a tooth!
When your popcorn is ready, measure all of your other ingredients and set them aside so that they are ready as soon as you need them. You will be busy stirring for a while, and so you do not want to worry about trying to measure your ingredients at the same time.
Make sure you chop up all of your Reese’s Peanut butter cups and place them in the freezer while you are preparing your popcorn. You want them to be in the freezer for at least 1 hour before you chop them and at least ten minutes after they are chopped.
When all of your ingredients are ready, then put your sugars into a pot and turn the heat on medium-low (on a smaller burner).
Begin stirring and don’t stop until the sugars are melted. If you let it sit, the sugars will begin to stick to the pan and to burn. It happens really quickly, so make sure you keep stirring!!
The sugars will go through various stages (about 5 minutes total). Initially it just looks like sugar. Then it starts getting hard and clumpy (don’t worry!! this is normal), then it will begin to melt. Make sure to stir constantly with a metal whisk or a wooden spoon (anything else can melt). When it is completely melted then add your butter.
It will go through stages again. Be patient and keep stirring! The sugar and butter will remain separated initially. That’s normal. Just keep stirring. Eventually it will begin to smooth out and any clumps will melt. It will become smooth and golden brown in color. DO NOT let it turn dark brown!! That means it is beginning to burn!
AS SOON as the butter and sugars and blended add your heavy cream . It will bubble up a little when the cold cream hits the hot caramel. Continue stirring until the is blended (it doesn’t take long at this point 1-2 minutes max).
Pour your caramel over your popped popcorn. Stir in half of your chopped Reese’s Peanut Butter cups. Put it in jelly roll pan or 9x 13 pan and bake on low (122°F/50°C) in your oven for approximately 30 minutes. Allow to cool slightly before adding the rest of your chopped peanut butter cups.