Preheat oven to 350°F. Line an 8- by 8-inch baking pan with aluminum foil, leaving a 2-inch overhang on 2 opposite edges. Cut a piece of parchment paper to fit the bottom. Lightly oil the parchment and the sides of the pan.

In a medium bowl, whisk together ground hazelnuts and baking powder. Set aside.

In the top of a double-boiler, over simmering water, melt unsweetened chocolate and butter. Stir constantly until chocolate and butter are fully combined and mixture is smooth. Set aside and cool about 5 minutes.

In the large bowl of an electric mixer, with speed set to high, beat eggs 2 to 3 minutes, until light and foamy. Add the sugars, vanilla and salt. Beat 1 to 2 minutes, until light and fluffy. Reduce mixer speed to low. Add the melted chocolate mixture. Mix until combined. Add the flour mixture. Mix until combined. Add chopped hazelnuts and chocolate chips. Mix until just combined. Spoon evenly into prepared baking pan. Smooth the top.

Bake for 25 to 30 minutes, until the top is firm to touch and the cookie is pulling away from the sides of the pan. The top should just begin to crack. Remove from oven, place on a cooling rack, and cool completely in the pan. When ready to serve, use the foil overhang to lift uncut bars from pan. Cut into 16 servings.

Store bars in an airtight container, at room temperature, for up to 3 days.

Baker’s Note: For a sweeter cookie, substitute bittersweet or semi-sweet baking chocolate for the unsweetened chocolate. Do NOT use chocolate chips.

Hazelnut Flour

Hazelnuts have been found in Mesolithic sites in Europe dating back to 7000 BC. They are rich in protein and unsaturated fats and have a balanced mixture of vitamins and minerals. Hazelnut flour imparts a deep aromatic nuttiness and intense richness to baked goods. It is naturally gluten-free, and is easy to make by grinding hazelnuts in a nut chopper or food processer.