Preheat the oven to 350 degrees. Spray a 9-inch springform pan with nonstick spray.
Heat the half and half in a large heavy-bottomed pot over low heat until you begin to see small bubbles forming around the edge. Add the chocolate and whisk until completely melted and smooth.
Whisk in the brandy, vanilla extract and the butter, a little at a time. Remove the chocolate mixture from the heat.
Place the egg yolks in a small bowl. Whisk them until they are smooth. Whisk in about 1/2 cup of the chocolate mixture, whisking constantly until blended. Pour the egg yolk mixture back into the chocolate mixture, whisking constantly until completely combined.
Pour the mixture into the prepared springform pan and bake for 20 minutes or until set.
Cool completely on a wire rack and then refrigerate until ready to serve.
Whip the cream to medium peaks. Cut the cake into thin slivers and garnish with a dollop of whipped cream and a sprinkle of toasted hazelnuts.