Grease a 9 inch by 13 inch baking pan. Preheat oven to 325 degrees F.

Place the flour in a small mixing bowl. Stir in the baking powder, salt, cinnamon, allspice, cloves, and nutmeg. Set aside.

Stir the sour cream with the baking soda and milk until smooth. Set aside.

Cream the butter with the granulated sugar and 1/2 cup brown sugar until blended well. Add in the egg yolks and the vanilla extract, and mix thoroughly.

Mix in the sour cream mixture, and blend well.

Add in the flour mixture, and mix until smooth.

Transfer cake batter into the prepared pan, and spread evenly.

In a clean mixing bowl, beat the egg whites until firm peaks form and add in the brown sugar gradually. Continue beating until stiff peaks form. Fold in the chopped pecans. Spread this over the top of the cake batter.

Bake in preheated oven for about an hour, until the topping is golden brown and the cake tests done.

Cool, and cut into serving size squares.