Preheat oven to 180ºC . Combine first 5 ingredients in mixing bowl and beat together with electric mixer. Combine remaining ingredients except the hazelnuts in another bowl. Sprinkle into the wet mixture a bit at a time and beat in with the mixer until velvety smooth.Lightly oil 9 in. cake pan. Sprinkle the bottom with flour. Pour in half of the batter, then sprinkle it evenly with half of the hazelnuts. Pour in the remaining batter and top with the remaining hazelnuts. Bake for 25 to 30 min., or until tests clean. Cook, and cut into wedges.