Sift together flour, sugar, baking powder, baking soda and salt. Separately combine egg, buttermilk and vanilla; beat until smooth and add butter. Combine mixtures and add hazelnuts. Mix. Place in a greased 8x8x2-inch pan and bake at 375 for 25 minutes or until done. To make glaze, melt butter and stir in sugar, buttermilk, syrup and baking soda. Boil over medium heat for five minutes; remove from heat and stir in flavoring. Poke holes in cake about 1/2-inch apart and pour warm mixture over cake. Cool before cutting. Best served at room temperature.