Preheat oven to 350°F. Grease a 9-inch spring-form pan with butter. Whisk together flour, cocoa powder, baking soda, and kosher salt in a medium bowl. In the bowl of an electric mixer, whisk together granulated sugar, egg, and melted butter. Add in 1 cup red wine and vanilla extract. Add flour mixture to the wet and whisk to combine. Scrape batter into prepared pan, and bake until a toothpick inserted in center comes out clean, 45-50 minutes. Let cake cool completely. Make the frosting by mixing powdered sugar, butter, vanilla, cocoa, and red wine together until blended completely and spread-ably thick. Place in the refrigerator if needed to thicken. Spread frosting on top, then garnish with chopped pistachios. Cut into wedges and serve.