1. Heat oven to 350°F. Lightly grease cookie sheet or line with parchment paper.
2. Combine cake mix, egg, oil and 3 tablespoons water in large bowl; mix with spoon until thoroughly blended. Stir in small chocolate chips. Combine 2/3 cup batter, chocolate packet from cake mix and remaining 1 tablespoon water; mix well. Drop vanilla batter by rounded teaspoons onto prepared cookie sheet. Press thumb gently into center of each cookie. Drop rounded half teaspoons chocolate batter into each thumbprint.
3. Bake 10 to 12 minutes or until very lightly browned. Cool slightly; remove from cookie sheet to wire rack. Cool completely. Makes about 36 cookies.