Add the sugar, water and lemon juice into a heavy-bottomed saucepan, mix until it resembles wet sand, and place it on your stovetop. Let the sugar melt and caramelize to a deep amber color over medium high heat.
Meanwhile, pour the heavy cream into a microwave-safe bowl and heat until hot, but not boiling.
When the sugar syrup has caramelized, pour in the hot heavy cream (do it in 2-3 batches to prevent the mixture bubble too much). Whisk vigorously until fully incorporated.
Remove from the heat and add the butter. Whisk vigorously until completely incorporated.
Add the salt and vanilla extract and whisk.
Use right away or pour into a clean, dry mason jar and store for future use.