Ensure the unsalted butter and heavy cream are at room temperature. Measure out all ingredients and have them ready.
In a heavy bottomed saucepan, pour the water into the pan and then pour the sugar on top avoiding the sides, and then add ¼ teaspoon lemon juice. Stir gently to moisten the sugar, but do not stir once it begins heating.
Place the saucepan over medium high heat. Allow the mixture to come to a boil without stirring. Watch closely as it cooks.
Continue heating until the sugar mixture turns a deep amber color. You can gently swirl the pan to move the caramel around and ensure even coloring, but avoid stirring. This process should take around 8-10 minutes. Do not let it darken too much, as it can taste burnt.
Once the caramel reaches the desired color, immediately remove the saucepan from the heat.
I like to wear an oven mitt to protect my hand from the steam. Carefully add 5 tablespoons of room temperature unsalted butter to the caramel. Stir gently until fully incorporated. Then, slowly pour in ½ cup of room temperature heavy cream, stirring continuously. The mixture will bubble up; keep stirring until smooth.
Stir in 1 teaspoon of vanilla extract and 1 teaspoon of sea salt. Mix until well combined. If you want a thicker caramel sauce, return to the heat and low boil it for 1 minute.
Allow the caramel sauce to cool to room temperature before transferring it to clean, airtight jars. Store in the refrigerator for up to 2 weeks. If the sauce thickens, gently warm it before using.