In a glass measuring cup, measure the heavy cream then add the butter. Warm in the microwave to melt the butter and set aside.
Add the sugar, corn syrup, water, and lemon juice to a large glass bowl and stir to combine.
Place the bowl in the microwave and run it on high, setting the timer for 6 minutes. After about 2 1/2 to 3 minutes begin checking the color of the boiling syrup by opening the door. Once a small area begins to turn amber, remove the bowl from the microwave and set it on the counter or onto something light colored that can withstand the heat.
The syrup will continue to bubble and change colors, deepening in amber. Keep a close eye on the color changing. If it appears the color has stopped changing (can happen in cooler weather), microwave for 15-30 seconds more to restart the change.
Once the color has reached a desired shade, very slowly add a small amount of the warmed cream and butter. The mixture will likely bubble up. Carefully stir everything together, add more cream/butter, combine well, add the remaining cream/butter, vanilla, and salt. Mix thoroughly.
Cool to room temperature then store in the refrigerator. The caramel sauce will thicken as it chills so reheat as needed to serve.
Notes
Substitution suggestions (untested by me):- Equal amounts of honey or golden syrup for the corn syrup- Equal amounts of buttermilk for the heavy cream- Equal amounts of apple butter for the butter- Add in a dash of cinnamon, nutmeg, any favorite spicesAdapted from Baked by Rachel.