Chocolate-Pistachio Torte

Ingredients

• 1/2 cup (1 stick) unsalted butter, cut into small pieces, plus more for pan
• 1 cup all-purpose flour, (spooned and leveled), plus more for pan
• 1/2 teaspoon salt
• 1/4 teaspoon baking powder
• 8 ounces semisweet chocolate, coarsely chopped
• 1 1/4 cups sugar
• 1 teaspoon pure vanilla extract
• 2 large eggs
• 1/2 cup low-fat buttermilk
• 3/4 cup shelled, unsalted pistachios, coarsely chopped
• 1/2 cup heavy cream
• 4 ounces semisweet chocolate, coarsely chopped
• 1/4 cup shelled unsalted pistachios, coarsely chopped