In a small pan, combine raspberries, erythritol, and lemon juice.
Cook over medium-high heat until the raspberries break down, about 8 minutes.
Combine xanthan gum, coconut flour, and water in a small bowl, then add the mixture to the raspberries, stirring until combined.
Once the raspberry sauce has thickened a bit (after about 2 minutes), transfer it to the fridge to cool completely.
Begin making the vanilla ice cream once the sauce is cooled.