Sweet potato cake with buttermilk glaze

For the cake:
3 ¼ cups plain flour
2 tsp. baking powder
½ tsp. bicarb soda
½ tsp. ground nutmeg
½ tsp. salt
½ cup milk
1 tsp. vanilla extract
225g unsalted butter, at room temperature
1 cup sugar
1 cup brown sugar
4 large eggs
2 cups mashed cooked sweet potato

For the buttermilk glaze (optional):
½ cup buttermilk
½ cup sugar
4 Tbsp. (55g) unsalted butter, cubed
1 ½ tsp. cornstarch or flour
¼ tsp. bicarb soda
1 tsp. vanilla extract

Preheat the oven to 175. Grease and flour a Bundt pan.

In a medium bowl, combine the flour, baking powder, baking soda, nutmeg, and salt. Whisk well. In a small bowl or measuring cup, combine the milk and vanilla.

In a large bowl, beat the butter, sugar, and brown sugar until light and fluffy. Add the eggs one at a time, beating well after each addition. Add the sweet potatoes, and mix until the batter is combined. (The batter may look terrible at this point: curdled, weird, terrible. Don’t worry.)  Fold in half of the flour mixture. Then add half of the milk mixture, and beat on low until well blended. Add the remaining flour, followed by the remaining milk, and beat on low until the batter is thick and smooth.

Scrape into the prepared pan, and bake for 60 to 75 minutes, or until a toothpick inserted in the center comes out clean. Cool the cake in the pan on a wire rack for 20 minutes, then carefully invert onto a rack.

Meanwhile, make the glaze. In a medium saucepan, combine the buttermilk, sugar, butter, cornstarch, and baking soda. Place it over medium heat, and bring it just to a gentle boil. Immediately remove it from the heat, stir well, and set it aside to cool to room temperature. Add the vanilla, and stir well.

Set the wire rack - with the cake atop it - over a rimmed sheet pan. Spoon the glaze over the warm cake.