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