Preheat the oven to 350°F. Butter and flour a 9- or 10-inch bundt pan (plain or decorative).
In a large bowl beat butter and sugar, Beat in the eggs one at a time. Beat in the vanilla and sour cream.
In a medium bowl combine the flour, baking powder, baking soda, cinnamon and salt. Stir the dry mixture into the butter mixture just until combined. Scrape into the prepared pan and spread so the top is even.
Bake for about 45 minutes, or until a wooden skewer inserted into the middle of the cake comes out clean. Let cool for 10 minutes in the pan on a wire rack, then flip the cake out of the pan and let cool completely on a wire tack.
While the cake is cooling, in a small bowl stir together the confectioners sugar, milk and vanilla until smooth. When the cake is cool, transfer to a serving platter and use a teaspoon to drizzle the icing back and forth in a pretty zig zag pattern across the top of the cake.
Notes
This is the perfect cake to have on hand for houseguests or neighbors dropping by for coffee. It's so easy to leave it out with a cake server so everyone knows to help themselves when they want just a little something sweet.