Start with a completely clean heavy bottom saucepan. Lightly spray the inside with non-stick spray to prevent sugar crystals splashing up and sticking to the sides.
Add the granulated sugar and water to the pan and place the pan over medium-low heat. Stir with a spatula until the sugar is dissolved and the water turns clear.
Increase the heat to medium and stop stirring completely. Watch as the sugar syrup turns from clear to light golden brown. When you see the color of the sugar start to change, watch it very closely the entire time so it doesn't burn.
While the sugar is cooking, add the heavy cream to a glass measuring jar and microwave in 30-second intervals until simmering.
As soon as the sugar turns dark golden amber in color, take the pan off of the heat and add in the butter. Stir until the butter is melted, then slowly pour in the warm heavy cream while stirring with a rubber spatula. Be careful because the caramel is very hot and it will bubble up when you add in the cream.
Stir in the salt and transfer the caramel to a glass bowl to cool.