If using sweetcorn-on-the-cob, shuck the cob using a sharp knife. Then place the sweetcorn in boiling water, to which a pinch of sugar has been added. Allow the water to come back to a boil and then wait 3 - 5 minutes before removing the corn from the water. Drain excess water, add a dollop of butter to the kernels and set aside. Skip this step if using canned or frozen sweet corn.