Sift flour into a bowl. Add sugar, salt and yeast. Combine and add melted butter. Add shredded Maca and onion. Pour milk, gradually, alternating with the eggs and continue stirring until a soft (not sticky) dough is obtained. Form portions with hands and let them rest, covered for 40 minutes. When the dough has doubled in size, form small rolls with floured hands. Bake in preheated moderate oven to 350ºF (180ºC) until done.