I highly recommend using this icing with a bundt cake, as it really brings out the details in the shape.
1 cup butter
3 cups sugar
6 tbs milk
1 tsp salt
1 tsp vanilla
Melt the butter in a medium saucepan over low heat. Grind the sugar in a food processor and add it to the butter. Add the milk and salt, and whisk to combine. Cook on low heat for ten minutes, stirring often, until the sugar granules have mostly dissolved. Remove from heat and stir in vanilla.
If you want to dye the icing, now is a good time to do it.
Allow icing to cool for about an hour or two, and then stir to create an even consistency. The texture will be thick and gritty. Drizzle over your cake and give half an hour to set.