Blackberry Velvet Gothic Cake

Ingredients

• 2 cups all-purpose flour
• 1/2 cup unsweetened cocoa powder
• 1 1/2 teaspoons baking powder
• 1 teaspoon baking soda
• 1/2 teaspoon salt
• 1/2 cup unsalted butter, softened
• 1 1/2 cups granulated sugar
• 2 large eggs
• 2 teaspoons vanilla extract
• 1 cup buttermilk
• 1/2 cup blackberry jam
• 1/2 cup hot water
• 1/2 cup fresh blackberries (optional, for garnish)
• 1 cup unsalted butter, softened
• 4 cups powdered sugar
• 1/4 cup seedless blackberry jam
• 1 tablespoon heavy cream
• 1 teaspoon vanilla extract
• Pinch of salt