1. Set the apple on the cutting board. The stem should be facing up.
2. Insert a short, thin bladed knife directly into the top of the apple. You should insert it about one centimeter from the center of the apple to avoid inserting it directly into the core.
3. Push the blade all the way through the apple. Do it slowly, so you don't cut yourself. Make sure that the knife pokes through the bottom of the apple, so you can see the blade.
4. Pull out the knife. Do this slowly and carefully. Watch where you place your fingers. If the knife does slide out more quickly than you expect, the blade should not go anywhere near your fingers or palm.
5. Repeat this process three more times around the center of the apple. When you're finished, you should have made four incisions to create a square around the center of the apple.
6. Insert the knife back into one of the incisions. Drag it from the first incision to the second, and all the way through the other two incisions, until you have completely cut around the apple's core.
7. Remove the knife and push out the core with your thumbs. Push it down through the apple until it pops out.