Cut all the cheeses and the margarine into pieces, melt them in the pot, stirring very well, (burns easily). Add the baking soda. When the mixture thickens, add whipped cream and sour cream and stir until the mixture is absolutely smooth.
Finally, add caraway seeds to taste. Now very important: stir until it is completely cool.
Under no circumstances should a skin form. So stir, stir, stir!