In a small bowl, combine warm water and yeast. Allow it to sit for about 5-10 minutes until it becomes foamy, indicating that the yeast is active.
In a large mixing bowl, whisk together the flour, sugar, and salt. Create a well in the center and add the frothy yeast mixture, milk, melted butter, egg, and vanilla extract.
Mix until the batter is smooth but don’t overmix; some lumps are okay. Cover the bowl with a kitchen towel and let it rise in a warm place for about 30-45 minutes or until it doubles in size.
Preheat your cast-iron skillet over medium heat. Lightly grease the skillet with butter or cooking spray.
Once the skillet is hot, drop about a tablespoon of batter for each mini pancake onto the skillet. Cook for about 1-2 minutes on one side, until bubbles start to appear on the surface.
Flip the poffertjes using a spatula and cook for another 1-2 minutes until golden brown on the other side.
Transfer the cooked poffertjes to a serving plate and keep warm while you repeat the process with the remaining batter.
Dust the poffertjes with powdered sugar and serve warm, optionally topped with fresh berries.
Notes
Serve warm with powdered sugar and fresh berries for an extra touch.