Officially it's probably wise to sift the flour but I couldn't find the sieve so didn't do that part. It worked fine... Add the yeast and the sugar to the lukewarm milk and let it dissolve. Make a little hole in the flour and put the yeast mixture in. Stir it all together and gradually add the rest of the milk, the (beaten) eggs and a little bit of melted butter to give the dough the desired consistency. Stir once more.
Let the dough rise for 45 minutes to 1 hour, under a humid cloth in a warm place.
Put the poffertjes griddle on the stove and lightly grease the cavities. Fill them only halfway or less with the dough (and that is the tricky part!!) Bake the poffertjes quickly until they are golden brown, then use a fork to turn them around, baking the other side golden brown as well. Arrange the baked poffertjes on a warm plate. Dust with powdered sugar and put a lump of butter on them before serving. Serve hot!