Add blueberries, sugar, salt and orange juice to a large pot and bring to a boil over medium-high heat, stirring occasionally.

Once boiling, remove from the heat and carefully add to a blender, or to a container to use with your immersion blender. Blend - carefully - then return to the pot. (Don't blend the hot liquid right on the stove or it can splatter all over your kitchen. Learn from my laziness.)

Return the mixture to a low boil and cook for 7-10 minutes. The sauce will thicken and should adhere to the back of a spoon when you run your finger across it (see picture above).

Remove from the heat. Skim the foam if needed (I usually don’t) and stir in the vanilla. Let cool.

You can strain the sauce through a fine-mesh strainer to make it more smooth or to remove any blueberry skins, if you have some remaining. Otherwise, pack the sauce up in jars and store - see notes below for details.