Place the whipping cream and the vanilla into a small-sized saucepan and bring to a boil over medium heat. (This step can also be done in a microwave using a microwave-safe bowl.) Cover and set aside until needed.
Add the water, sugar, corn syrup, and salt into a medium-sized pot. Combine with a spatula, then cover with a plate and bring to a boil over medium-high heat.
Continue to boil the sugar mixture, swirling the pan occasionally until the mixture turns a golden amber colour.
Remove the pot from the heat and carefully pour the warm cream into the hot sugar, whisking constantly until combined. Be sure to wear an oven mitt on your stirring hand, as there can be lots of steam, and the caramel will bubble and splatter.
Add the lemon juice and whisk until combined. Then add the butter and whisk until the mixture is well combined.
Transfer the caramel to a medium-sized bowl and use as directed in the recipe.
Place any leftover caramel in an airtight container and store in the fridge for up to 3 weeks.