1. Trim both ends from a medium onion. Place cut-side down on a cutting board and slice in half.
2. Remove and discard outer layers. Place on half, rounded side up, on board. Place your palm flat over curve of onion.
3. Holding knife parallel to board, make 1 or 2 slices (lengthwise) into onion.
4. Shape your hand into a claw and make 3 to 4 cuts straight down into the onion, leaving one end slightly attached.
5. Change direction and slice straight down, following curve of onion half. Repeat with remaining half.