Work the margarine, sugar, eggs, flour, baking soda and cocoa powder into a smooth dough. Fold in the sour cream with a spoon. Fill the dough into molds and bake in a preheated oven at 180 ° C for about 20 minutes. Let the muffins cool completely on a wire rack.
In the meantime, melt the chocolate in a water bath for the glaze, let it cool down briefly, then stir in the sugar and sour cream. Spread the icing on the muffins and allow to set in the refrigerator before serving.