Combine the sugar, water, and corn syrup in a large, heavy saucepan. (Make sure your pan is large because the caramel will get very bubbly.)
Cook over medium heat, stirring occasionally, until the sugar has dissolved. Bring the mixture to a boil. Stop stirring, and allow the mixture to cook until it’s a deep golden amber color and reaches 350°F (175°C). This will likely take 8 to 12 minutes. Don’t stir during this time, but you can gently swirl or rotate the pan if needed to help it cook evenly.
Remove the pan from the heat. Add the cream slowly and steadily while whisking with a long-handled whisk. The mixture will bubble quite a bit during this step. If the mixture hardens and seizes, return it to low heat and whisk until smooth.
Stir in the butter until thoroughly combined.
Allow the caramel sauce to cool completely before storing. It will thicken as it cools.
Notes
*You can use salted butter if you want a salty bite to your caramel.
Store the cooled caramel in an airtight container in the refrigerator up to 2 weeks. Let it come to room temperature or warm it briefly in the microwave before serving.