Preheat your oven to 350°F (175°C) and prepare a 9x13-inch baking pan by greasing it with oil or butter and dusting it with flour.

In a large mixing bowl, combine mashed sweet potatoes, granulated sugar, brown sugar, vegetable oil, eggs, buttermilk, and vanilla extract. Blend until smooth.

Sift together flour, baking powder, baking soda, salt, and spices in a separate bowl, then stir to combine.

Gradually add the dry ingredients to the wet mixture, stirring gently until just combined.

In a small bowl, mix granulated sugar and ground cinnamon for the swirl, then set aside.

Pour half of the batter into the prepared pan, sprinkle half of the cinnamon-sugar mixture, add remaining batter, and swirl gently.

Bake for 35-40 minutes until a toothpick inserted comes out clean. The top should be golden-brown.

Cool the cake completely in the pan on a wire rack.

Whisk together powdered sugar, milk, and vanilla extract for the glaze until smooth.

Once cooled, drizzle the glaze generously over the cake and serve warm or at room temperature.