Peel and dice the potatoes and stew them in a pot covered with a little water for about 15 minutes until soft. Drain the potato, put it back into the pot and let it evaporate briefly on a switched off hotplate.
Mash potatoes with a fork.
Line recesses of a muffin tray (12 recesses) with paper cups. Mix flour and baking powder well in a bowl. Lightly whisk the eggs. Add sugar, salt, oil and milk and mix well.
Add flour mixture and stir briefly, fold in sweet potato. Spread the dough into the troughs and bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 25-30 minutes.
Take it out, put it on a cake rack. Let it rest in the mould for about 10 minutes. Lift the muffins out of the trough and let them cool down.
Chop the chocolate and melt it over a warm water bath. Put some chocolate on each muffin. Chill the muffins until the chocolate has set. Whip the cream until stiff, fill into a piping bag with star-shaped spout.
Spray generous tuffs on the muffins. Chop the nuts and sprinkle them on the muffins.