In a small heavy saucepan, combine butter, 1/4 cup whipping cream, and brown sugar. Heat over medium heat, stirring frequently, until butter is melted.
Evenly divide butter mixture between 2 9-inch cake pans. Sprinkle evenly with chopped pecans.
In a large mixing bowl, combine cake mix, water, oil, and eggs. Beat for 2 minutes at medium-high speed.
Carefully spoon batter into the 2 cake pans.
Bake for 35 to 40 minutes, until cake springs back when lightly touched in middle.
Cool for 5 minutes. Remove from pans and cool completely. (Note: do not let cool in the pans for longer than 5 minutes they will start to stick as the sugar mixture on the bottom cools.)
To make topping, in a small saucepan combine 1/2 cup whipping cream, cornstarch, and 1/4 cup sugar. Heat over medium heat, stirring constantly until mixture begins to simmer. Immediately remove from heat and pour into a bowl. Let cool to room temperature.
Place a mixing bowl and whisk attachment for electric mixer in the freezer of refrigerator.
Once cornstarch mixture has cooled, remove mixing bowl and whisk attachment from freezer, add 1 1/2 cups very cold whipping cream to the bowl and beat until it starts to thicken. Gradually add cornstarch mixture. Turn mixer to high and beat until cream is very thick. Beat in vanilla.
To assemble, place 1 layer on a cake stand pecan side up. Cover with half of the whipped cream. Top with second layer, pecan side up and cover with remaining whipped cream. Decorate with pecans and chocolate curls.
Notes
Wrap well and store in the refrigerator for up to 4 days.Nutritional info is provided as an estimate only and will vary based on brands of products used.