Preheat oven to 350°F (180°C). Spray a 9-inch springform pan with baking spray with flour. Line bottom and sides of pan with parchment paper.

In a large bowl, whisk together cornmeal, flour, granulated sugar, finely chopped hazelnuts, brown sugar, baking powder, and salt. Using hands, a pastry blender, or 2 forks, cut in cold butter until mixture is crumbly and butter is the size of small peas.

In a small bowl, whisk together eggs and vanilla bean paste; add to cornmeal mixture, and mix with hands until combined but mixture is still crumbly. Sprinkle half of dough crumbles (about 421 grams) evenly into bottom of prepared pan, very gently patting (but not pressing) into an even layer.

In a small microwave-safe bowl, heat chocolate hazelnut spread on high in 10-second intervals, stirring between each, until loose and fluid. Spoon chocolate hazelnut spread into a small pastry or resealable plastic bag; cut a ½-inch opening in tip or corner. Pipe over dough in pan, leaving about a ½-inch border; smooth into an even layer as needed. Sprinkle remaining dough crumbles evenly on top, pressing into clumps as desired. Top with chopped hazelnuts.

Bake until golden brown and set, 35 to 40 minutes, rotating pan halfway through baking and loosely covering with foil during final 5 to 6 minutes of baking to prevent excess browning. Let cool in pan on a wire rack for 10 minutes. Remove sides of pan; let cool completely on pan base on a wire rack. Use a serrated knife to cut and serve.