Preheat oven to 180°C (approximately 350°F). Heat 350 grams (approximately 12 ounces) chestnut puree. Stir in butter and cinnamon. Separate eggs. Mix egg yolks with sugar for about 5 minutes or until light and flurry. Stir in chestnut puree.
Grease pan with butter. Beat egg whites with salt until stiff. Fold into batter along with hazelnuts. Pour half of batter into pan and spread remaining chestnut puree on top. Pour remaining batter over puree and smooth. Bake for 30-35 minutes. Cool briefly, remove from pan and cool completely on a wire rack. Garnish with sweetened chestnut puree and candied chestnuts. Slice and serve.