Preheat oven to 350º
Melt 4 T of butter in small saucepan; stir in brown sugar; heat until bubbly. Stir in corn syrup and cream; heat, stirring constantly, just to boiling. Add nuts; pour into a generously-buttered 10 inch bundt pan. Do not use baking spray. Use butter. Lots of butter. Let stand while preparing cake.
Sift flour, powder and salt onto waxed paper
Beat remaining butter in large bowl until soft, gradually beat in granulated sugar until well combined. Beat in egg yolks, chocolate and vanilla until well combined.
With mixer on low, mix in flour mixture and milk, alternating. Beginning and ending with flour. (Do not skip and add all at once)
Beat egg whites until stiff; fold into cake batter.
Spoon batter evenly over the nut mixture in the pan.
Bake 45 minutes or until cake is done. Do not cool in pan. Loosen the cake from edges of pan and invert on serving plate. Scoop out any nuts and syrup remaining in pan and smooth onto cake. Serve warm with whipped cream.
Rewarm cake to soften top if it becomes to stiff to cut.