Place paper cups in the 12 holes of the muffin baking tray. Cream butter and sugar with the whisk of the hand mixer. Stir in the eggs one by one. Sift flour, cocoa and baking soda over them and stir in briefly.
Preheat oven (electric cooker: 175°C/circulating air: 150°C/gas: level 2). Put 1 tbsp. of dough into each of the tins. Put 2 toffees in each and spread the rest of the dough on top. Bake in a hot oven for 15-18 minutes.
Let it cool down.
Coarsely chop the couverture, melt with the cream in a hot water bath. Spread half of the muffins with chocolate icing, dust the other half with icing sugar.