1Heat oven to 325°F. Spray 10-inch tart pan with removable bottom with cooking spray. Make brownie batter as directed to box using water, oil and egg. Pour 1 2/3 cups brownie batter into pan.
2Bake about 18 minutes or until toothpick inserted 2 inches from side of pan comes out moist. Place pan on cooling rack; cool completely, about 45 minutes.
3In medium bowl, beat yogurt, hazelnut spread and vanilla with whisk until smooth and creamy. Spread evenly over cooled brownie. Garnish with chopped hazelnuts. Refrigerate until ready to serve.