Rhubarb Cake

2 tablespoons soft butter
3/4 cup light brown sugar
1 teaspoon vanilla
1 egg
1 1/4 cup all-purpose flour
1/2 teaspoon baking powder
1/4 teaspoon salt
1/2 cup sour cream
2 cups chopped rhubarb

Toppings:
About 6 lumps sugar
1/2 teaspoon mace

In a bowl beat together the butter, brown sugar, vanilla, and egg. Mix the flour, baking powder, and salt in the top of a sifter, set over the butter-mixture bowl, then sift into the bowl alternately with the sour cream. Blend well, then fold in the rhubarb. Spread the batter into a greased 8-inch square pan. Crush the sugar lumps and mix with the mace. Sprinkle over the top of the batter and bake in a preheated 350 degrees f oven for 45 minutes.