Slice onion length wise, leaving the root end on! Slice off the opposite end to remove onion peel.
With the tip of your knife, slice from root end to base. Be careful not to go too close to the root
Slice parallel cuts into the sides 3/4 of the way to the root (~5-6 cuts depending on size of onion)
Now slice all the way through perpendicular to your cuts as small or large as you desire