In a medium bowl, mix together the margarine, masa flour, and sugar until light and fluffy. In a food processor or blender, blend one cup of the corn kernels with the water and cornmeal just until smooth. Stir into the masa mixture. Mix in the remaining corn, baking powder, salt, and milk until the batter is smooth. Pour into a double boiler.
Place the tomalito over a large saucepan of simmering water, and cover tightly with aluminum foil. Steam for 50 to 60 minutes, or until firm. Check water occasionally, and refill if necessary. Stir pudding before serving to give it a consistent texture. Serve in small scoops.