Put flour into a bowl and create a well in the middle. Dissolve yeast and 1 teaspoon sugar in some lukewarm milk and pour into well. Knead into flour to form a thick dough. Cover and let rest in a warm place for about 30 minutes.
Knead in butter, remaining sugar and lemon zest. Add remaining milk and egg. Cover again and let rest for 30 minutes. Knead again and shape into dumplings. Brush with melted butter and let rest 30 minutes more.
Bake in an oven preheated to 180°C (approximately 350°F) for 25-30 minutes, until golden brown. Remove and let cool slightly. Dusted with powdered sugar and serve.