Step 1: Equipment
You'll need a head of celery, a sharp chef's knife or santoku knife, and if you want to get extra fancy, a vegetable peeler (more on that later).
Step 2: Separate Stalks
Separate the individual stalks from the bunch by gently prying them out from the bottom until they snap off.
Step 3: Clean and Trim
Wash the individual stalks under cold running water to remove any dirt and debris, then trim off the large white section off of the bottom of each stalk. Reserve for stock, compost, or discard as you wish.
Step 5: To Cut Large Chunks
Large chunks are primarily used for stocks and sauces which will eventually be strained, or for rustic stews. Using your chef's knife, cut the stalks into 1 to 1 1/2-inch pieces.
Step 6: Stop at Joint
Stop cutting at the joint where the main stalk meets the beginning of the leafy sections. Save this section for stock.
Step 7: For Thin Slices
For slices to use in salads or sautees, cut into 1/8th to 1/4-inch half-moons crosswise.
Step 9: For a Fine Dice
For fine dice, use the tip of your chef's knife to split the stalk lengthwise, keeping it attached at the leaf end (cutting it crosswise into two or three shorter sections can help if this step is difficult for you at first).
Step 10: Continue Splitting
Split the stalk a few more times. The total number of splits will determine the size of your final dice. For medium dice, split once in half. For finer dice, split into quarters. For brunoise, split every 1/8th to 1/16th inch or so.
Step 11: Cut Dice
Rotate the celery stalk and cut crosswise to form fine dice. The split section of the stalk should hold together as you cut.
Step 13: Done
Batons, large dice, slices, and fine dice ready to cook or incorporate into salads.