Gather all of your ingredients and have them nearby ready to add to the mixture as needed. In a heavy-bottomed 3 quart saucepan, heat sugar and water over moderately high heat whisking constantly to dissolve sugar.
Once mixture reaches a boil, stop whisking and allow mixture to boil until it reaches a dark amber color, carefully swirling pan occasionally.
Once mixture reaches a dark amber color, immediately add butter and whisk until butter has melted then immediately remove from heat. Wait 3 seconds then carefully pour in cream and immediately whisk to combine (it will bubble vigorously).
Whisk until mixture is smooth. Allow caramel to cool several minutes then pour into a glass jar to cool. Sprinkle lightly with sea salt after spooning caramel over cheesecakes.