In a large mixing bowl, combine the all-purpose flour, sugar, salt, and yeast. In a separate bowl, whisk together the milk and eggs until smooth. Gradually pour the wet mixture into the dry ingredients, stirring gently until just combined.

Cover the bowl with a clean kitchen towel and let the batter rise for approximately 30 minutes at room temperature. The surface should be bubbly and the volume increased significantly.

Heat a poffertjes pan or a non-stick skillet over medium heat and lightly grease each well with butter. Pour small dollops of batter into each well and cook for 2-3 minutes until the bottoms are golden brown, then flip and cook for another 1-2 minutes.

Remove the poffertjes from the pan and transfer them to a serving platter. Dust generously with powdered sugar and serve warm with a pat of butter on top.