Preheat your oven to 350°F (175°C). Grease and line two 8-inch or 9-inch cake pans with parchment.

In a large mixing bowl, combine all-purpose flour, granulated sugar, unsweetened cocoa powder, baking powder, baking soda, and salt.

In another bowl, whisk together eggs, vegetable oil, buttermilk, and vanilla extract until smooth.

Pour the wet mixture into the dry ingredients and stir just until combined. Be careful not to overmix.

Add the hot water to the batter and mix well.

Divide the batter evenly between the prepared cake pans and bake for 30–35 minutes, until a toothpick comes out clean.

Let the cakes cool in the pans for about 10 minutes, then transfer to a wire rack to cool completely.

In a saucepan over medium heat, combine blackberries and 1/4 cup of granulated sugar. Stir until the blackberries become juicy.

Mix cornstarch with water to form a slurry, then add to the saucepan with lemon juice. Cook until thickened, then let it cool.

Once cooled, place one cake layer on a serving plate. Spread blackberry filling on top.

Add a layer of whipped cream followed by the second cake layer. Top with more whipped cream.

Decorate with fresh blackberries, dark chocolate shavings, and edible flowers.

Refrigerate the assembled cake for at least one hour before slicing.