Place rhubarb in a greased 10-in. cast-iron or other heavy ovenproof skillet. Combine sugar, flour and nutmeg; sprinkle over rhubarb. Drizzle with butter and set aside
For batter, in a large bowl, beat the butter and sugar until blended. Beat in the egg. Combine the flour, baking powder, nutmeg and salt. Gradually add to egg mixture alternately with milk, beating well after each addition until completely combined.
Spread batter over the rhubarb mixture. Bake at 350° until a toothpick inserted in the center comes out clean, about 35 minutes. Loosen edges immediately and invert onto a serving dish. Serve warm. If desired, serve with vanilla ice cream, whipped cream or a big glass of milk.
Enjoy!