I call the top of the onion the half that the stem grew up from. The bottom is where the roots grow out.
1. Peel the onion.
2. Cut the onion straight through the top and bottom. You should have half of the root on each side.
3. Place the onion in the freezer. If you're only using half of the onion for your recipe, store half in the fridge for a later use.
4. After a few minutes, take half of the onion out of the freezer.
5. Place it flat side down on a cutting board.
6. With a sharp knife, cut the top tip off of the onion.
7. Hold your knife parallel to the cutting board.
8. Slice horizontally through the onion from the top towards the roots, but not through them.