Dissolve the yeast, sugar and several tbsp flour in part of the warm water. Leave the yeast to bubble. To this mixture, gradually add the remaining water, 1/5 cup (60 g) of butter, the salt and flour.
Knead a soft dough. Divide it into 4 equal parts. Roll out a very thin sheet from each one, smear with the remaining butter and wrap into a roll.
Divide each roll into 3 equal parts and cut each of those in half lengthwise but not all the way through. Wrap each one into a snail shell and put them in muffin forms.
Leave them to rise, then bake at 356°F (180 °C) until golden. Before serving, sprinkle with powdered sugar.