Pistachio Chocolate Soufflé

Ingredients

• ½ cup / 100 g sugar, granulated
• 2 tablespoons / 30 g water
• 1 teaspoon / 6 g kosher salt
• ⅓ cup / 45 g pistachios, coarsely chopped
• 1 cup / 240 g heavy cream
• ⅓ cup / 80 g pistachio butter
• 2 ¼ cups / 385 g dark chocolate chips (66% to 70% Cocoa)
• 7 tablespoons / 100 g butter, unsalted plus more for coating ceramic ramekins
• ½ cup / 120 g pistachio butter
• 6 each / 120 g egg yolks
• ¾ cup / 150 g sugar, granulated
• ¼ teaspoon / 1 g cream of tartar
• 1 ¾ cups / 380 g egg whites