Step 1: Place the wasabi in a nonreactive mixing bowl. Add 1 tablespoon of cold water and stir to form a thick paste. Let sit for 5 minutes to develop the flavor.
Step 2: Add the mayonnaise, sour cream, lemon juice, and soy sauce and whisk to mix. The mixture should be thick but pourable. If necessary, thin with a little more water. If not using immediately, cover and refrigerate. Place in a plastic squeeze bottle for serving.