Pour cold milk into the jug, up to the bottom of the spout, but remember to purge the steam wand first. Place the wand about a ½ inch or 1.5cm into the milk. Open the steam valve and lower the jug to introduce air to the surface of the milk. A Flat White should have a thinner layer of microfoam compared to a Latte or Cappuccino.
Aim for a temperature of around 140-150F, or 60-65C. A good manual indicator would be when the milk jub becomes too hot to touch. For non-dairy, try not to go over 130F, or 55C, as the milk can start to separate or curdle. Look for a velvety and silky-smooth texture. Swirl the jug and then tap it on the counter to ensure the milk is integrated and the bubbles removed.