For the sauce: Add the frozen cherries, sugar and 2 tablespoons water to a small saute pan over medium heat and stir to combine. Add the brandy and flambe or cook until the alcohol burns off. Add the lemon juice, vanilla extract and a pinch of salt. Bring the mixture to a boil, then reduce the heat to a simmer and cook until the cherry sauce is thick and bubbly, about 20 minutes. Remove from the heat and allow the sauce to cool, about 10 minutes.
For the pudding: Mix together the pudding and whipped topping in a small bowl.
For the cake: Spread the butter generously on both sides of the pound cake slices. Toast the cake in a dry frying pan over medium-low heat, 1 minute per side. Spoon the boozy cherry sauce over the toasted pound cake and finish with a dollop of the whipped chocolate pudding. Sprinkle with shaved dark chocolate.