Pre-heat the oven at 180 degree temperature. Grease 2 tin of 8 inch size with little oil/butter and sprinkle some flour on top.
Mix together flour, cocoa powder, baking powder, baking soda and sift them through a sieve so that there are no lumps.
In a mixing bowl, whisk together butter and 150 grams caster sugar with the help of electric beater until they are fluffy. Gently add eggs and whisk again. Now add the dry flour mix slowly and whisk again. Add milk and whisk again to form a smooth batter.
Pour this batter into both the greased tins, tap them 2-3 times and place the tins in the oven and bake it for approximately 35 minutes.
Keep 8-10 blackberries aside and put rest of them in a pan. Add rest of 35 grams (approx. 3 tablespoon) sugar to it and let them cook on medium high heat. Once sugar is melted, crush the blackberries with the help of spatula. Cook this mixture for 10 minutes until most of the water is evaporated from the compote. Switch off the heat and let it cool for few minutes. Once its lukewarm, strain it through the sieve to extract all the seeds. Keep the compote aside and let it cool completely.
After 35 minutes, check the cake by inserting toothpick/knife in centre. If it comes out clean, take out the tins and let them cool. If the cake is not done yet, cook for few more minutes until its cooked completely.
Once the tin is cool enough, flip them over and take the cake out and cool it completely. Slice both the cakes horizontally from middle. This way we will have 4 equal pieces of cake.
In a mixing bowl, add whipping cream and whisk it with electric beater until you get stiff peaks. Now gently mix half of that blackberry compote in it with the help of spatula.
Take one slice of cake and spread the whipped cream evenly all over it. Now pour little amount of blackberry compote in middle and spread that too. Place another slice of cake on it and repeat the process.
Finally, when all 4 slices are used, Spread cream all over the cake so that whole of the cake is covered. Smooth it out with the spatula or knife. Decorate with any design of piping nozzle and garnish with rest blackberries and edible flowers.