• Wash the raspberries. Whisk the cornstarch and water together in a small bowl. This is your cornstarch slurry. Set a medium-sized bowl with a fine mesh strainer next to the stove.
• Place the raspberries in a 3 or 4-quart saucepan and add the lemon zest, lemon juice, kosher salt, and granulated sugar. Place the pan over medium-high heat. Cook the raspberries until they begin to boil, stirring occasionally. Reduce the heat to medium and simmer for 10-15 minutes until the liquid is reduced by a third and noticeably thicker.
• Stir the cornstarch slurry into the raspberries and increase the heat to medium-high. Continuously stir the raspberry sauce until it comes to a boil and then boil it for 30 seconds.
• Remove it from heat and pour the raspberry sauce into the strainer and use a large spoon to press the sauce through the strainer to remove the seeds. Stir in the vanilla extract. Cool the sauce to room temperature. Once it’s cool, refrigerate the sauce. You can serve the sauce while it is still warm.

Storage

• The raspberry sauce can be stored in the refrigerator for up to one week.