1. Preheat oven to 350 degrees F. Line a 9-by-13-inch baking pan with foil, making sure there's a 2-inch overhang on both short sides. Gently press the foil into the corners, and spray the foil with cooking spray.
2. If hazelnuts are not toasted, place them on a small rimmed baking sheet and bake, shaking the pan once or twice, until lightly golden, about 5 to 8 minutes. Remove nuts from pan and set aside.
3. In a large bowl, whisk together flour, baking soda, and salt.
4. In a large saucepan, melt butter over low heat. Stir until smooth, then remove from heat. Stir in brown sugar and vanilla. Stir in eggs, one at a time, until fully blended. Stir in flour mixture just until incorporated. Stir in hazelnuts.
5. Spread batter in prepared pan. Drop small spoonfuls of chocolate hazelnut spread evenly over the batter. Using a butter knife, gently swirl spread into the surface of the batter; be careful not to cut through the foil. Bake until golden brown and the spread swirls look mostly dry, about 26 to 28 minutes. Cool completely in pan.
6. When cool, hold the two foil ends, lift the bars from the pan and turn onto a cutting board; peel off foil, then turn right side up. Cut lengthwise into quarters, then cut crosswise into 8 strips to yield 32 bars. Store in an airtight container.
Source: Hannaford fresh Magazine, July - August 2015