I use a bowl and a whisk because if you do it this way you will have pieces of shallot and garlic in the final vinaigrette. The shallots will become marinated the longer it sits. Giving a nice crunch and flavor in a salad. You can do this with an immersion blender, food processor or blender but the shallot and garlic will get chopped fine and imparting a more garlic and shallot flavor in the vinaigrette.