Preheat the oven to 180°C and line a 12-hole bun tin with paper cases.
Whisk softened butter until fluffy then beat in the sugar.
Gradually whisk the beaten eggs into the butter mixture to avoid splitting.
Sift and fold the flour into the cake batter using a metal spoon.
Stir in the vanilla, salt, and enough milk to reach a soft dropping consistency.
Divide the batter equally among the paper cases until half full.
Bake in the center of the oven for 15 minutes until golden-brown.
Transfer the cakes to a cooling rack to cool completely.
Whisk butter, icing sugar, milk, and vanilla together until creamy for the icing.
Cut tops into wings, pipe buttercream into the centers, and assemble with jam or curd.