Preheat oven to 350 degrees. Grease and flour a ring mold or baking dish (9x9). Mix together the margarine and sugar in a large bowl. Add the egg and beat it in well. Next, stir in the molasses. Then measure the boiling water in the molasses measuring cup and add it to the mixture, stirring well. Measure all tahe dry ingredients into a small bowl, starting with the flour and ending with the baking soda. Stir all the dry ingredients together, then mix thoroughly into the liquid. Pour immediately into the prepared ring mold. Bake for 40 to 45 minutes, or until a skewer stuck into the cake comes out clean. If you are using a ring mold, let the cake cool for about 5 minutes, then unmold onto a plate. To make the whipped cream, put the chilled cream in a small chilled bowl, add the sugar and lemon extract and beat with an electric mixer until stiff. To serve put a dollop of whipped cream over each slice of warm cake.