Place a clean, sturdy cutting board on a flat surface. Make sure your knife is sharp, clean, and ready to use.

Place your onion on the cutting board. Carefully trim off the stem end, but leave the root end intact. This helps hold the onion together while you slice.

Slice the onion in half from the root end of the onion to the stem end. Your knife must be sharp to prevent crushing or tearing the onion layers.

Peel off the papery skin of the onion from both halves and throw it away.

Place the two onion halves flat-side down on the cutting board. This creates a stable surface for slicing, preventing the onion from rolling around.

With both cut sides of the onion facing flat-side down, begin making vertical cuts crosswise. Aim for uniform slices of your desired thickness, whether paper-thin for salads or thicker for sauteing.

Once you've finished slicing the first half of the onion, move on to the second half and slice it the same way. Make sure to be consistent with the size of the slices.