Preheat oven to 160C fan-forced. Line 3 x 22cm cake pans with baking paper.
Place flour, cocoa, sugar, baking soda, baking powder and salt into a bowl and combine.
Then place oil, eggs, vanilla and plum powder into a stand mixer fitted with a paddle. Combine.
Add flour mixture in and coffee. Combine on medium speed for 15-20 seconds until glossy and uniform.
Pour evenly into cake pans. You can weigh the batter to make it easier then ladle equal portions into each pan.
Bake for 20 minutes or until a skewer comes out clean. Turn cakes out onto a wire rack to cool.
While the cakes are baking and cooling. Clean your mixer bowl and paddle attachment then add butter and icing sugar to it. Cream together for 4-5 minutes on medium speed until pale and creamy. Add milk and beat again for a further minute. Make sure you scrape your bowl down if you need to.
Set this aside.
Once your cakes are cold, add one to a plate or cake stand. Spread with an even layer of buttercream then top with jam. Add the next cake layer on top gently pressing down. Repeat the process then add the top layer. Use the remainder of the buttercream to frost the top and sides of the cake. Set it in the fridge to firm then top with Davidson plums and Davidson plum powder to serve.
You can bake the cake one at a time if you have one cake pan, just divide the batter evenly.
You can thin your jam out with some water if it’s too thick to easily dollop over the buttercream.
You can use regular fresh or canned plums if Davidson plums are not in season.