Make these mini rum bundt cakes to serve as part of a dessert buffet or on their own as favors for wedding guests to take home.
Preheat oven to 325 degrees. Generously spray mini Bundt cake pans with cooking spray. Sift together the flour, baking powder, and salt in a medium bowl. Combine buttermilk and rum in a glass measure.
Cream butter and both sugars in a mixer bowl on high speed until light and fluffy, about 3 minutes. Add eggs one at a time, beating well between each; mix on medium speed until combined. Add flour and buttermilk mixtures, alternating between them, and beginning and ending with flour.
Fill each cake pan with about 1/2 cup batter; tap pan against the counter to remove any air bubbles and to evenly distribute batter. Bake until tops spring back when touched lightly, edges begin to pull away from pan, and a cake tester inserted in the centers comes out clean, 18 to 20 minutes. Transfer pan to a wire rack for 15 minutes; then invert pan to unmold cakes onto rack. Let cool completely.
To serve, whisk together glaze ingredients until smooth, and drizzle 1 1/2 tablespoons over each cake.