Preheat an oven to 350 degrees F (175 degrees C). Grease an 8 inch cake pan and line with a circle of parchment paper.
Beat the margarine and sugar with an electric mixer in a large bowl until light and fluffy. The mixture should be noticeably lighter in color. Add the eggs one at a time, allowing each egg to blend into the margarine mixture before adding the next. Fold in the flour until only small lumps remain; pour into the prepared pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 30 minutes. Cool in the pan for 10 minutes before removing to cool completely on a wire rack.