Creating Blackberry Velvet Cake can be straightforward if you follow these simple steps:

1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
2. Mix Dry Ingredients: In a large bowl, sift together the flour, granulated sugar, cocoa powder, baking soda, and salt.
3. Combine Wet Ingredients: In another bowl, whisk together the vegetable oil, buttermilk, eggs, vanilla extract, blackberry puree, and vinegar until fully combined.
4. Combine Mixtures: Gradually add the wet ingredients to the dry ingredients, stirring until the batter is smooth and free of lumps.
5. Divide Batter: Pour the batter evenly into the prepared cake pans.
6. Bake: Place the pans in the preheated oven and bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.
7. Cool: Remove the cakes from the oven and let them cool in the pans for about 10 minutes. Then, transfer them to wire racks to cool completely.
8. Prepare Frosting: In a mixing bowl, beat the softened butter until creamy. Gradually add powdered sugar and heavy cream, mixing until smooth and fluffy.
9. Assemble the Cake: Once the cakes are cool, place one layer on a serving platter. Spread a layer of frosting on top, then place the second layer on top.
10. Frost the Top and Sides: Use the remaining frosting to cover the top and sides of the cake.
11. Garnish: Decorate with fresh blackberries on top for an elegant finish.

These steps will guide you in creating this incredible Blackberry Velvet Cake effortlessly.