First, I get all the ingredients measured out and ready to go before I start to cook the sugar. Measure the cream, cut the cold butter into tablespoon-sized slices, and set aside the salt all near or on the stove. 

Pour the sugar into a medium saucepan (preferably copper or stainless steel) and set over the stove over medium heat. Stir with a whisk continuously until the sugar begins to brown and stick together.

The sugar will first change from sugar to sugar spheres as they start to stick together and then eventually turn into a brown liquid during a 10-15 minute period of time. Whisk continuously during these transitions. Take out the whisk and switch to a small spatula once the sugar gets really sticky.

Once the sugar has become a complete liquid, stop stirring and put a candy thermometer in until the caramel hits 350 degrees.

Then immediately and carefully add the butter until it is completely melted. Remove from the heat and slowly add the cream while continuing to stir. It will bubble vigorously, so be careful. Pour into a tempered glass bowl and let cool at least 15 minutes before using.