Prepare the pudding according to package directions but use less milk as the ingredients state above. The filling should be thicker then if you were just making a pudding.
FOR THE CAKE:.
In a mixing bowl sift the flour, baking powder and salt.
In another bowl cream the potato and margarine together. Add sugar and beat until sugar is fluffy and incorporated into the mixture.
Add the vanilla and lemon extract and continue beating.
Slowly add the soy milk and beat until well mixed. Add the flour mixture, 1/3 cup at a time and beat until the batter is smooth.
Pour the batter into your prepared pan and bake for 25 to 30 minutes, or a tooth pick comes out clean inserted in the center.
If done, remove cake from oven and cool on a metal rack for 20 minutes. Remove the cake from the pan and cool for an additional hour on the cooling rack.
Cut the cake in half. Fill it with the vanilla pudding, put the top back on the cake and glaze.
FOR THE GLAZE:.
Combine the melted margarine, cocoa and hot water in a bowl. Blend in the confectioner's sugar and vanilla. When you like the consistency pour or spread over the cake and let it cool for a while so the glaze can set.