Combine half the sugar and water in a small saucepan and heat until the sugar is dissolved. Take off the heat and add the cranberries, shake the pan gently until the cranberries are well coated in the syrup. Remove from the pan with a slotted spoon and lay them out on a wire rack to dry for one hour. Then toss them with the remaining sugar.
For the cake
Preheat your oven to 350 F/180 C, butter and line 3 8"/20cm cake pans with parchment paper or spray with a cake release spray.
Mix together flour, sugar, cocoa, baking powder, baking soda and salt in a large bowl until combined. In a separate bowl mix eggs, milk, oil and vanilla. Add the wet ingredients to the dry ones and beat with an electric mixer until well incorporated.
Divide evenly among 3 pans and bake in the preheated oven for 25 minutes until a toothpick comes out clean. Bake 2 layers together and then the third one later if your oven isn't big enough to fit three cake pans.
Cool in the pans for 10 minutes, then remove cakes from the pans and cool completely on a wire rack.
For the cranberry compote
In a small saucepan combine the cranberries, sugar, water and port and cook on low heat until the mixture thickens and coats a spoon for about 10 minutes. Cool slightly and process in a food processor or blender until smooth. Set aside until needed. Alternatively, you can leave the cranberry compote chunky if you wish.
For the whipped ganache
Heat the heavy cream in a small saucepan but take it off the heat right before it boils and pour over chopped dark chocolate. Let it sit for 1-2 minutes then stir with a whisk until well blended.
Let the ganache cool, then whip with an electric mixer until it's the consistency of a buttercream and paler in colour. (The ganache will not whip when it's still warm. It needs to be slightly chilled to whip properly.)
To assemble the cake
Pipe a border of the whipped ganache around each cake layer and fill with the cranberry compote as shown in photos, stack on top of each other and cover the top and the sides with a thin layer of the whipped ganache. Let it chill for 15 minutes. Then cover with more ganache or pipe rosettes all over and decorate with sugared cranberries. Store the assembled cake in the refrigerator but take it out 30 minutes before serving to allow the cake and the ganache come to a room temperature for fuller flavour and desired consistency. * I used Wilton 1M closed star tip to decorate
I recommend using the whipped ganache soon after it was whipped as it tends to harden, which will make it impossible to use a piping bag.