Chocolate and mint is one of the most timeless flavor combinations—and it really shines in this bundt cake recipe. Cake flour is the key to keeping each slice super light and fluffy.
Preheat the oven to 350 degrees.
Spray a 15-cup nonstick Bundt pan with cooking spray; set aside.
In a medium bowl, whisk cocoa with hot water until smooth. Whisk in sour cream; let cool. Into a medium bowl, sift together flour, baking soda, and salt; set aside.
In the bowl of an electric mixer fitted with the paddle attachment, beat butter and sugar on medium speed until light and fluffy, 3 to 4 minutes. Add eggs, one at a time, beating to combine after each; scrape down sides of bowl as needed. Beat in vanilla. With mixer on low speed, add flour mixture in two parts, alternating with the cocoa mixture and beginning and ending with the flour; beat until combined.
Pour batter into prepared pan; smooth with an offset spatula. Bake until a cake tester inserted in center comes out clean, 45 to 50 minutes.
Transfer pan to a wire rack to cool 15 minutes. Invert cakes onto rack; Re-invert cake; let cool completely, topside up.
Using a serrated knife, trim bottom of cake layer to make level. Transfer to a wire rack set over a rimmed baking sheet. Pour over ganache to cover. Let stand until set.