Having regularly sized slices is essential for an apple pie or tart to cook evenly. The easiest way to do this is to start by holding the apple on its flower end. Slice directly down one side, coming as close to the core as possible without actually getting to any of the core. Place the apple flat on the cut surface, then cut off the remaining three sides, rotating the apple as necessary, then discard the core. Holding one piece cut side down with your free hand, carefully cut it into slices, using the knuckles of your free hand as a guide. Take this with all of the apple pieces and cook immediately to avoid discoloration.