Place the raspberries, blueberries and blackberries in a bowl and sprinkle over 2 tsp flour.

Place the butter, brown sugar and granulated sugar in a bowl and beat with an electric mixer until pale and fluffy. Add the eggs one at a time, beating with each addition. Add the vanilla extract and wild berry jam and mix well.

Place 5 cups flour, baking powder and salt in a bowl and whisk together. Add this to the butter mixture in 3 additions, alternating with sour cream. Add the berries and gently mix into the batter.

Spray 3 9-inch round cake pans with cooking spray and divide the batter evenly between all pans. Place the cakes on the bottom rack of the oven and bake at 350F for 40 minutes, or until fully cooked. Cool the cakes in the pan for 10 minutes, then transfer to a cooling rack and cool completely.

In the meantime, make the buttercream. Into a small bowl place 1 ½ cups buttercream, the mixture of berries and wildberry jam. Combine and set aside to use as the filling. Place 2 tbsp of buttercream into a smaller bowl and add some black food colouring. This will be the black marks on the bark.

Set out 4 small bowls and place 1/3 cup of buttercream in each bowl. Place ½ teaspoon, 1 teaspoon, 1 tablespoon and 2 tablespoons of cocoa powder into the bowls and mix well. These will be the four colours for the tree rings. Place the buttercream for the tree rings and the black buttercream for the bark into individual piping bags and cut a small hole at the ends.

To assemble the cake, slice a thin layer off the surface of each cake to flatten them. Spread half of the berry buttercream filling in between each layer. Coat the entire cake in a thin layer of the remaining white buttercream and place the cake in the fridge for 20 minutes for the buttercream to stiffen.

Coat the cake in a thicker layer of the white buttercream. Using the black buttercream, make small horizontal lines and dots around the sides of the cake. Glide a clean knife over each line to smudge the buttercream, creating a birch bark effect. Make sure to wipe the knife clean with a paper towel after each use.

Draw rings using the 4 shades of brown buttercream onto the top of the cake, and enjoy!