Trim the Ends - Use a sharp knife to trim the stem end about ½-inch. Trim the root end to remove the strands, but keep the bulb intact. If slicing, trim ¼-inch off the root end.
Separate into Halves - Place the onion on a cutting board, stem-side down. Cut lengthwise down to create two halves. Place them cut-side down on the board.
Peel the Skin - Peel away the papery skin starting from the stem end. If needed, remove the first layer of the onion to make peeling easier.
To Cut an Onion
For Slices - Slice lengthwise, from root to stem, following the grain to yield firm pieces with a mild flavor. For softer pieces with more intense flavor, make cuts crosswise, horizontally against the grain. Repeat slicing with the other half.
For Wedges - Make radial cuts towards the center to give a wedge shape. Make 2 cuts for 3 large pieces, 3 cuts for 4 medium pieces, or 4 cuts for 5 smaller pieces. Repeat slicing with the other half.
For Rings - Make a ¼-inch slice lengthwise on the middle side. Place this cut-side on the board to stabilize the onion. Firmly hold and make cuts crosswise through the equator. Alternatively, a mandoline can be used to make rings.
To Dice an Onion
Traditional Method - Hold the halved onion with your fingertips. Alternatively, press down with your palm with fingers pointing up. Make about 1 to 3 cuts horizontally towards the root end but not cutting through, depending on dice size. Make vertical cuts down the onion lengthwise until about 1-inch from the root end. Rotate the onion so that the root end is in the back. Make slices down, perpendicular to the other slices, to dice. Cuts can be made vertically first, then horizontal if you feel more comfortable.
Angled Method - Make cuts lengthwise on the halved onion, about 60-degree radial cuts down towards the board, but not in the center of the onion. Make perpendicular cuts down to give the desired dice size.
Vertical Method - Cut the onion in half lengthwise to yield quarters. Work one by one and make vertical cuts, 1-inch from the root end on each piece. Flip so that the cuts are now horizontal. Make vertical cuts, 1-inch from the root end on the sides now facing up.Push two quarters together to form an onion half, or keep separate. Hold them together with the claw, and slice horizontally down to create diced pieces.
Notes
Yield: Small onion (2” wide) about ½ cup. Medium onion (2 ½ to 3” wide) about 1 cup. Large onion (4” wide) about 2 cups.
Diced Sizes: Minced (⅛-inch or smaller, fine (⅛ to ¼-inch), medium (¼ to ½-inch), coarse (½ to ¾-inch pieces).
Storing: Place cut onions in a glass container or a resealable plastic bag, then in an airtight container. Wrap leftover onion halves and pieces tightly in foil, then in a plastic bag or container. Refrigerate for 7 to 10 days. Freeze in a resealable bag for up to six months.