To slice an onion, peel and halve it first. Then, put the rounded side facing upward on the cutting board. Have the root end at the far end of your hand. Bend your fingers onto the onion half to hold securely, using your thumb to keep the onion from slipping. With a sharp kitchen knife, slice the onion evenly, keeping the knife tip in contact with the cutting board as you draw the knife through. Once most of the onion half has been sliced, and you're at the root end, turn the remaining piece of onion onto the largest flat side left and slice again––this prevents any from being wasted.