Step 1) Preheat oven to 350°F. Line 24 (2-1/2 inch) muffin cups with paper baking cups.
Step 2) Mix cake mix, oil, sour cream, eggs, and water in a large mixing bowl until smooth. Stir in vanilla.
Step 3) Divide batter evenly into prepared muffin cups. Place a chocolate kiss in center of each filled cup, pressing down lightly (top of kiss will still be seen).
Step 4) Bake 17 to 22 minutes or until a wooden toothpick inserted in center comes out clean. Cool in pans on wire racks 5 minutes. Remove; cool completely. Frost with Chocolate Buttercream Frosting.
Chocolate Buttercream Frosting:
Beat butter and cocoa powder together until well combined. Mix in powdered sugar, salt and vanilla. Add milk, one tablespoon at a time until spreadable consistency is reached.