Cream the softened butter with the sugar until very light and fluffy using a wooden spoon or electric mixer.
Dissolve the egg yolk in a small bowl.
In a small saucepan with a spoonful of water, melt the 100 g chocolate over very low heat. Once melted, remove from heat, stir in the milk and egg yolk mixture. Let cool, then incorporate into the butter-sugar cream. Beat until light and fluffy.
Butter the charlotte mould. Mix water and cognac on a plate. Arrange macaroons soaked lightly in this mixture: flat side against the bottom and walls of the mould.
Add a layer of chocolate cream. Repeat layers of soaked macaroons and cream, finishing with macaroons flat side up.
Cover with a plate and weight, refrigerate for 12 hours.
To serve, unmould onto a platter. Prepare glaze: melt 50 g dark chocolate in minimal water, add 50 g butter. Pour over the top, allowing drips down the sides. Serve very chilled.
Source: The 100 Best Desserts from Larousse
