You can either use an electric frother, hand mixer, blender, or jar to turn the rest of the oat milk into froth. Just add the remaining 3 oz. oat milk and gingerbread syrup together and froth, mix, blend, or shake until the mixture froths up a bit. Note that oat milk doesn't froth that well and the froth doesn't last long. See notes for alternative if you don't want oat milk froth.