Preheat oven to 300 degrees and grease a 9-inch square pan. Line pan with greased parchment or waxed paper. In a microwave-safe bowl, combine butter and chocolate and microwave 1-2 minutes or until butter is just melted. Stir until smooth. If chips are not quite soft, microwave for an addition 30 seconds. Mix in cocoa and reserve. Beat the eggs and the sugar until fluffy and pale in color, about 4 minutes. Add vanilla. Fold butter and chocolate mixture into the egg and sugar mixture. Gently fold in nuts. Pour into the prepared pan and bake for 35 to 40 minutes or until risen in center and edges start to get firm and shiny (center may still move and appear underbaked). Cool completely in pan on wire rack (center may sink slightly). Cover and refrigerate for 4 hours or overnight.

In a medium saucepan over medium heat, combine cocoa, sugar and water. Bring to a boil and let boil 1 minute. Remove from heat and stir in vanilla.

To make whipped cream:

Beat cold cream for 2 minutes. Add sugar and beat until very thick. Add vanilla and refrigerate until ready to assemble.

To Assemble:

Cut brownies into 12 or 16 squares. Set each square on an individual serving plate. Top with a scoop of vanilla ice cream, warm chocolate sauce, whipped cream and chocolate shavings.