Add all of the ingredients into a medium-sized saucepan. Cook on medium-low heat for 2 to 3 minutes, or until the raspberries start to soften.
Adjust the heat to a gentle simmer. Cook for 5 to 8 minutes, mashing the berries with the back of a wooden spoon, until thickened. The sauce will continue to thicken as it cools.
Store covered in the fridge for up to 1 week or freeze in a freezer-safe container for 3-6 months. Thaw on the countertop or in the fridge.