Place the pot roast in the slow cooker. I used the 3-quart crock pot slow cooker because my pot roast was small. If cooking a bigger pot roast use a slow cooker your pot roast fits in.
Sprinkle the Au Jus Gravy mix and the ranch dressing over the pot roast and add the ¼ cup of water.
Next add the stick of butter, baby carrots and the peperoncini peppers to the crock pot. (I sliced the peppers to hide them from a couple of picky eaters in my family but you can put the whole peppers into the crock pot if you don't have to hide them.)
Place the lid on the crock pot and cook for 4 to 8 hours on high (depending on how large your pot roast is) or 8 to 10 hours on low.
The pot roast is done when the meat is fall apart tender. My 2.5 lb eye round roast was cooked perfect at 3 and half hours.
When the pot roast is done cooking remove it from the slow cooker to a serving platter and allow it to rest for about 10 minutes before slicing.
Add the remaining ¾ cup of water to the slow cooker and stir into the juices.
In a small bowl mix the 1 tablespoon of water with the ½ tablespoon of cornstarch until all the lumps have dissolved. Pour the cornstarch slurry into the slow cooker and mix until the gravy begins to thicken. Place the cover on the slow cooker and allow the gravy to continue to thicken while you are slicing the pot roast.
Tip: slice the pot roast against the grain for the tenderest slices of pot roast you have ever eaten.