Split open the ¼ vanilla bean and scrape out the seeds.
Combine water, sugar, salt, and vanilla bean seeds and pod in a 3-quart saucepan over medium heat.
Stir the syrup until it comes to a boil.
Continue cooking until the syrup is a light golden color, swirling the pan for even caramelization.
Once the caramel is a light golden color, lower the heat and cook until the caramel is a light amber color.
While syrup is cooking, bring cream and salt to a simmer in a small saucepan.
When the caramel is a light amber color, turn off the heat and pour one fourth of the hot cream into the caramel. The caramel will bubble vigorously. When the bubbling slows, add the remaining cream.
If you're using vanilla extract, add it in now with the cream.
Let caramel sauce cool to room temperature.
Refrigerate for several weeks in an airtight container.