Homemade Rhubarb Upside-Down Cake

Directions

1. Preheat oven to 325°. In a small bowl, combine brown sugar and butter. Spread into a greased 10-in. cast-iron or other ovenproof skillet. Layer with rhubarb; sprinkle with sugar. Set aside.
2. In a large bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Beat in egg yolks and vanilla. Combine the flour, baking powder and salt; add to creamed mixture alternately with milk, beating well after each addition.
3. In a small bowl, beat egg whites and cream of tartar on medium speed until stiff peaks form. Gradually fold into creamed mixture, about 1/2 cup at a time. Gently spoon over rhubarb.
4. Bake until cake springs back when lightly touched, 40-50 minutes. Cool for 10 minutes before inverting onto a serving plate. Serve warm, with whipped cream or ice cream if desired.