For the mascarpone-chocolate cake:
1) Preheat oven to 160 to 170 degrees, gas mark 3.
2) In a large mixing bowl, cream butter and sugar until light and fluffy. Add eggs, 1 at the time, beating well after each addition. Add mascarpone and vanilla; mix well.
3) Combine the flour, cocoa, baking soda and salt; add to the creamed mixture alternately with buttermilk, beating well after each addition. Pour batter into a 25cm cake tin and bake for 45 minutes.
For the lavender-honey butter cream:
1) Cook sugar to a soft ball stage. Whisk the egg whites until stiff. Slowly pour cooked sugar into egg whites. Continue to whisk until meringue cools down to room temperature. One by one add small pieces of butter, then stir in the honey.
For the milk chocolate ganache:
1) Chop chocolate into small pieces and place into a bowl. Bring double cream to a boil and pour over the chocolate. Stir until all pieces are melted.
For the assembly:
1) Cut cake in 3 equal disks. Fill the first layer with the milk ganache and the second layer with the lavender-honey butter cream. Use the butter cream to frost the sides and top of the cake.