Preheat oven to 350°F then grease a 9-inch spring-form pan with butter.
Whisk together the flour, cocoa powder, baking soda, and salt in a medium bowl.
In the bowl of an electric mixer, whisk together the granulated sugar, egg, and melted butter.
Add in 1 cup red wine and vanilla extract.
Add the flour mixture to the wet mixture and whisk to combine.
Scrape the batter into the prepared pan and bake until a toothpick inserted in center comes out clean, 45-50 minutes.
Let the 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 it in the refrigerator for 5-10 minutes if it needs to thicken.
Spread the frosting on top, then garnish with chopped pistachios. Cut into wedges and serve.