01 - Preheat the oven to 350°F. Grease a mini bundt pan thoroughly with butter or nonstick spray.
02 - In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt. Set aside.
03 - In a large bowl, beat the softened butter and sugar together until light and fluffy, about 3 minutes.
04 - Add eggs one at a time, mixing well after each addition.
05 - In a separate small bowl, combine buttermilk, vanilla extract, vinegar, and green food coloring.
06 - Add half of the dry ingredients to the butter mixture, mixing just until combined. Pour in the buttermilk mixture; mix briefly. Add the remaining dry ingredients and mix until smooth.
07 - Spoon the batter evenly into the prepared mini bundt pans, filling each about two-thirds full.
08 - Bake for 18–22 minutes, or until a toothpick inserted into the center comes out clean.
09 - Cool cakes in the pan for 10 minutes, then carefully invert onto a wire rack to cool completely.
10 - Whisk powdered sugar, milk, and vanilla extract until smooth and pourable. Drizzle over cooled cakes.
11 - Decorate with green and gold sprinkles as desired.