Stir sugar, corn syrup, water, salt, and lemon juice together in a microwave-safe measuring cup or glass bowl.
Microwave until mixture reaches 320 to 330 degrees and just begins to change color, about 5 to 8 minutes.
Let the caramel sit for 5 minutes to darken to a honey brown color.
Stir in hot cream a few tablespoons at a time, then add butter.
Serve immediately or refrigerate.
