Preheat the oven to 375.
Grease and flour a 9x9 inch baking pan.
Cream the butter and then add the sugar and cream together.
Add the molasses and sour cream or yogurt and blend well.
In a small bowl, blend the flour, baking powder, baking soda, salt and ginger.
Add the dry ingredients to the wet and blend well, beating until smooth.
Pour the cake batter into the prepared pan and bake 30-40 minutes, until a toothpick comes out clean from the center of the cake.
Let the cake cool at least 5 minutes before removing from the pan or just let it cool completely in the pan.
Sprinkle with powdered sugar before serving if you'd like.