Rhubarb Upside Down Cake

I got this recipe from http://homejoys.blogspot.com/2013/05/rhubarb-upside-down-cake.html

2 cups fresh rhubarb (approx. 3/4 lb.)

1 cup brown sugar

2 tablespoon butter

1/4 cup butter

1 cup sugar

1 egg

2 cups flour

2 1/2 teaspoon baking powder

1/4 teaspoon salt

1 cup milk

1 teaspoon vanilla

Choose fresh, crisp rhubarb. Chop rhubarb into 1/4-1/2″ pieces. Melt butter in a medium-size skillet over low heat. Add brown sugar and diced rhubarb. Continue to fry for 2 more minutes. Remove from heat and set aside. If you are not using a cast iron skillet remove the rhubarb from the pan to a small baking pan.

Batter: In a small mixing bowl cream together butter and sugar. Add egg and vanilla, mix until incorporated. Combine flour, salt, and baking powder. Add flour mixture and milk to batter and mix until combined. Pour batter over the rhubarb. Bake at 375 degrees for 40 minutes. Remove from oven, and run a knife along the edges to loosen cake. Turn upside down onto a plate. Serve hot or cold with milk or cream if desired.