Melt the chocolate in a double boiler at a low simmer, stirring occasionally. Add the espresso powder and mix to combine. Remove from the heat and let cool until cool to the touch, about 10 minutes.
Whip the cream, sugar and vanilla to soft peaks in a large bowl, then let sit at room temperature for about 10 minutes.
Meanwhile, whip the egg whites in a separate large bowl until they hold soft peaks. Set aside.
Take a large spoonful of the egg whites and mix into the chocolate mixture to lighten. Gently fold the remaining egg whites in. Fold in the whipped cream until no white streaks appear. Divide among glasses or bowls. Top with Blackberry Sauce, grated chocolate and whipped cream, if using.
Combine the blackberries, sugar and lemon juice in a saucepan over medium-high heat. Bring to boil, then lower to a simmer and cook until the berries soften and break down, about 10 minutes. Mash the berries with the back of a spoon or a potato masher. Add the liqueur and cook for an additional 2 minutes. Strain through a mesh sieve. Let cool slightly before using.