Melt the butter with the milk

• Melt the butter in a saucepan or microwave.
• Whisk the warm melted butter together with the milk until smooth.

Make the yolk batter

• Whisk the egg yolks and vanilla extract into the butter-milk mixture.
• Sift in the flour and whisk until the batter is smooth and lump-free.

Whip the egg whites

• Beat the egg whites until foamy, then add the sugar gradually.
• Whip to soft to medium peaks.

Fold the batter

• Fold a third of the meringue into the yolk batter to loosen it.
• Gently fold in the remaining meringue until just combined, keeping the air in.

Prepare the water bath

• Pour the batter into a lined baking dish and smooth the top.
• Place the dish in a larger pan filled with hot water and cover with a lid or foil.

Air fry covered

• Air fry at 150 °C with the lid on.

Air fry uncovered

• Remove the lid and continue air frying at 150 °C until golden and set.

Cool and slice

• Let the cake cool in the dish, then lift it out and slice.