1. Pour cream into a heavy saucepan. Split vanilla bean in half and use the tip of a sharp knife to scrape the seeds from he pod. Add beans to the cream. Place over med high heat and bring to just under a boil, stirring occasionally. Reduce the heat and keep cream warm.
2. In a heavy saucepan, combine sugar, water, salt & corn syrup. Bring to a boil over med heat, stirring to dissolve the sugar. Cook without stirring, until the mixture is amber colored, 5-8 minutes. Watch this or it will burn. Remove from heat.
3. The mixture will continue to cook off heat so work fast. Slowly add the cream to the sugar syrup. This will bubble so be careful. Let the mixture simmer down and then whisk until smooth. Add lemon juice. Let cook 10 minutes
4. Cut the butter into tablespoons and add to caramel, one at at time, whisking to constantly. Then whisk caramel periodically until cool.
The caramel will keep in an airtight container in fridge for one month