In a saucepan, whisk together the wet ingredients.
Add in the dry ingredients.
Turn heat to medium-low and cook, whisking constantly, until it thickens slightly (about 5–7 minutes). Keep it at a gentle heat. Do NOT boil hard—arrowroot can lose its thickening power if overheated.
Remove from heat and stir in vanilla extract.
Let sit 10–15 minutes.
Pour into molds and freeze 6–8 hours or overnight.
