Prepare the 12" x 17" sheet pan by lining it with parchment paper. Leave some parchment overhang so you can easily lift the caramel out when finished.
In a heavy duty, thick bottomed pot, combine all ingredients EXCEPT for the instant oatmeal.
Cook over medium heat while constantly stirring until butter melts and sugar dissolves.
Increase heat to medium high for the remainder of cooking. You must stir the whole time.
Cook until temperature reaches 240F. This takes approximately 40 minutes. 220-230F will take the longest, with the temperature going quickly between 230F and 240F.
When you hit 240F, turn off the heat. Add the instant oatmeal and stir for one minute.
Pour on prepared sheet pan. Spread into an even layer.
Allow to cool to the touch (can still be warm, but hot piping hot). Cover with parchment paper and foil until ready to use. Do not refridgerate.