In a small bowl, dissolve the yeast in lukewarm milk. Let it sit for about 5 minutes, or until foamy. This step is essential, as it activates the yeast and ensures a light, airy texture in the dough.

In a large mixing bowl, combine the flour, sugar, and salt. Make a well in the centre and pour in the activated yeast mixture, egg, vanilla extract, and melted butter. Mix gently with a wooden spoon or whisk until the batter is smooth and lump free. The consistency should be thick but slightly sticky.

Cover the bowl with a clean kitchen towel and let the batter rest for 45 minutes in a warm place. This allows the yeast to work, developing air pockets that will give the croustillons their signature fluffiness.

Once the batter has risen, heat vegetable oil in a deep fryer or a heavy bottomed pot to 180°C (350°F). To check if the oil is ready, drop a small spoonful of batter into the oil, if it sizzles and rises quickly to the surface, the oil is at the right temperature.

Using a spoon or a small ice cream scoop, carefully drop small portions of batter into the hot oil. Fry in batches to avoid overcrowding the pan, which can lower the oil temperature and make the dough absorb too much grease.

Fry the dough balls for about 3 to 4 minutes, turning them occasionally with a slotted spoon to ensure even browning. They should puff up and develop a deep golden brown crust.

Once cooked, transfer the croustillons onto a plate lined with paper towels to absorb excess oil. Let them rest for a few seconds before moving on to the final step.

Dust generously with powdered sugar while still warm. The slight heat helps the sugar stick to the dough balls, creating the classic light coating.

Serve the croustillons immediately while warm and crispy. Traditionally, they are enjoyed plain, but they pair beautifully with a side of melted chocolate, fruit preserves, or a drizzle of honey for extra indulgence.