Preheat oven to 350 F and line 1 - 12 ct cupcakes tin with cupcakes liners.
In a medium sized bowl, sift the flour, cocoa powder, baking powder and baking soda then add the chopped rosemary. Stir to distribute.
In a bowl of a standing mixer fitted with the paddle attachment, place the sugar, eggs and oil. Sprinkle the flour on top.
With the mixer on low-medium speed as the ingridients starts to come together, add the warm milk and warm heavy cream and mix just until all has evenly incoporated.
Turn mixer off and gently fold in the chocolate chips.
Fill the cupckes liners with cupcakes batter just 3/4 full. Bake for 15 minutes or until a toothpick comes out clean from the center of the cupckes.
Remove from stove and let cool.
Mash the Blackberries in a sieve on-top of a medium bowl until only the seeds remain. Discard the seeds.
Place the egg whites in a bowl of a standing mixer fitted with the cage attachment.
Place 1 cup of sugar and the water in a pan and let cook on top of medium heat until it reahces 240F.
Once the sugar mix reaches 210F, beat the egg whites until frothy and sprinkle the remaining ¼ cup sugar.
Slowly drizzle the sugar syrup in the egg whites and beat on high until the bowl is cold to the touch.
Add the butter 1” cube at a time and beat until you have a smooth and creamy buttercream.
Add the blackberry puree 1 TBS at a time and mix to incorporate.