sweetened whipped cream or whipped toppingoptional
Preheat oven to 350 degrees F. Coat the bottom and sides of a 10" springform pan generously with non-stick cooking spray.
Scatter the sliced rhubarb over the bottom of the prepared pan. Combine 1 cup sugar, 2 tablespoons flour, 1/2 teaspoon cinnamon and 1/4 teaspoon nutmeg in a small bowl and sprinkle it over the rhubarb. Drizzle 1/4 cup melted butter over the top and set it aside.
For the batter, in a large bowl, beat 1/4 cup melted butter and 3/4 cup sugar until blended. Beat in the egg. In a separate bowl, combine the flour, baking powder, cinnamon, nutmeg and salt. Add about half of the dry mixture to the egg mixture and beat just until combined. Add half of the milk and beat again until combined. Repeat with remaining flour mixture and milk, beating well. Spoon the cake batter over the rhubarb mixture and use an offset spatula or the back of a spoon to spread out evenly.
Bake for 40 to 45 minutes or until golden brown and a toothpick inserted in the center comes out clean. Remove from oven and run a knife along the edge of the cake and the pan to loosen the edges and then immediately invert onto a serving dish. Unlatch and remove the sides of the springform pan. Use a knife to lift up the base of the pan and remove it.
Allow to cool for about 10 to 15 minutes and then slice and serve warm with whipped cream, if desired.
Rhubarb should be trimmed by about 1" at each end. Trim and discard green leaves. Wash well and slice into 1/2" slices.