Crackled-topped Rhubarb Coffee Cake

Cake

 * 2 cups all-purpose flour
 * 1 cup granulated sugar
 * 4 tsp baking powder
 * 1 tsp ground cinnamon
 * ½ tsp salt
 * 1 large egg
 * 1 cup buttermilk
 * ¼ cup vegetable oil, preferably canola oil
 * 2 tsp pure vanilla extract
 * ½ lb (2 cups) rhubarb, trimmed and cut into ½-inch pieces

Topping

 * ¼ cup granulated sugar
 * ½ tsp ground cinnamon

Cake

 * 1) Preheat oven to 350°F.
 * 2) oil lightly an 8-inch square baking pan or spray with nonstick cooking spray.
 * 3) Set aside.
 * 4) Sift flour, sugar, baking powder, cinnamon and salt into mixing bowl.
 * 5) Whisk together egg, buttermilk, oil and vanilla in a separate bowl.
 * 6) Add flour mixture to egg mixture, and stir with a rubber spatula or wooden spoon just to blend.
 * 7) Stir in rhubarb.
 * 8) Turn batter into prepared pan, spreading evenly.

Topping

 * 1) Stir together sugar and cinnamon.
 * 2) Sprinkle evenly over top of cake.
 * 3) Bake for 45 to 50 minutes, or until top is brown and crackled and a toothpick inserted in center comes out clean.
 * 4) Remove from oven, and cool in pan on a wire rack for 15 minutes.
 * 5) Cut into squares, and serve while still warm.