Dark Romance Chocolate Blackberry Cake

Ingredients:
For the Cake:
2 cups all-purpose flour
2 cups sugar
3/4 cup unsweetened cocoa powder
2 teaspoons baking powder
1.5 teaspoons baking soda
1 teaspoon salt
1 teaspoon espresso powder
1 cup milk (or buttermilk, almond, or coconut milk)
1/2 cup vegetable oil (or melted coconut oil)
2 large eggs
2 teaspoons vanilla extract
1 cup boiling water
1 cup fresh blackberries, chopped (extra whole for decoration)
For the Blackberry Frosting:
1 cup unsalted butter, softened
4 cups powdered sugar
1/2 cup blackberry puree (from fresh or frozen blackberries, strained)
1 teaspoon vanilla extract
A pinch of salt
Purple or aubergine food coloring (optional)
For the Glossy Ganache:
1 cup heavy cream
1 cup dark chocolate, finely chopped
2 tablespoons light corn syrup or honey
1/2 teaspoon vanilla extract (optional)