Set the oven to 180°C (160°C fan, gas mark 4). Grease and line 2 x 18cm /7in round sponge tins.
Place the butter, chocolate chips and milk into a pan and heat until everything is melted and smooth.
Remove the pan from the heat and stir in the sugar. Beat the egg into the crème fraiche then stir into the cake mix, followed by the flour and baking powder.
Whisk the egg whites in a clean grease free bowl until they form stiff peaks. Fold the egg whites into the chocolate cake mixture taking care not to knock out all the air.
Divide the cake mix between the two tins, then bake for 25-30 mins until the mixture feels just firm in the centre. Leave to cool for 5 mins then turn out and allow to cool.
To make the rich chocolate icing, melt the chocolate in a mixing bowl over (but not touching) a pan of gently simmering water (or in a microwave).
Remove the chocolate from the heat and stir in the butter and cream until smooth. If necessary, chill the icing until it is firm enough to spread.
Sandwich the two cakes with a little of the icing, then spread the remainder over the top and sides of the cake.
To make the chocolate paste roses, very gently melt the chocolate in a mixing bowl over (but not touching) a pan of gently simmering water (or in a microwave).
Remove the chocolate from the heat, stir the liquid glucose and water into the chocolate, stirring until smooth and thick. Place in a plastic bag and chill in the fridge until firm. It will set very hard. Remove it from the fridge half an hour before using.
To make chocolate roses, cut the paste into small pieces and knead each piece until soft and pliable. Make a small cone for the rose and stand it upright on the work surface. Roll small pea size balls of chocolate icing between cling film until flattened, pinch one edge a little thinner than the other and wrap the petals around the cone, overlapping to make a rose. If liked cut the base off the rose before placing on the cake.
Sprinkle some silver Boll.
To make leaves, roll oval leaf shapes, mark the veins with the back of a knife and pinch one end to give it some shape then add to the roses on top of the cake. The icing will make about 20 roses.