Gather the ingredients.
Trim and peel kohlrabi and carrots. You can use a vegetable peeler on carrots, but to properly peel kohlrabi, you’ll have better luck with a paring knife: Trim tops and bottoms of kohlrabi and set flat bottoms on a cutting surface; use a sharp paring knife to cut down from top to bottom, removing thick, tough peel (with this method you’ll easily be able to see where tender white-ish inside ends and the green or purple peel begins, working around vegetable until all the peel is removed). Set peeled vegetables aside.
In a salad bowl or large mixing bowl, whisk together oil, vinegar, mustard, and salt until well blended. Add pepper, if you like.
Using large holes on a standing box grater or a mandoline set up for fine julienne, grate kohlrabis and carrots into salad bowl.
Toss everything together until kohlrabi and carrot are evenly coated with dressing. Taste and add more salt or pepper, if you’d like.