Combine the vinegars, water and vanilla powder. Pour into a 500 ml (17 fl oz/2 cup) capacity jug. Insert a hand-held stick blender into the mixture but ensure there is no air trapped underneath the blades by tilting the stick blender to the side to release any air — you don’t want to draw any air into the mixture and create bubbles. Return the stick blender to an upright position with the blades firmly on the base of the jug and blend the stock on the slowest setting — this will help prevent the stock ‘whirlpooling’ and drawing in air. While blending, add the xanthan gum very slowly, a bit at a time. It helps to use a parfait spoon (long-handled teaspoon) to maintain control and avoid the xanthan clumping. It’s best to just very gently tap the spoon on the side of the jug while blending. Set aside until needed.