Preheat the oven to 180°C (fan-forced, 160°C).
Start by preparing your ‘Tinkie’ moulds: cut a 20 cm x 30cm strip of heavy-duty foil and fold in half. Place a cylindrical-shaped spice bottle in the middle and fold the sides of the foil up to almost enclose the bottle. Fold the ends up like you’re wrapping a present. Gently remove the spice bottle and you’ll be left with a cylinder-shaped Tinkie mould! Repeat until you have 10 of them, then grease well with cooking spray and arrange in a brownie pan.
To make the sponge, whip the eggs, sugar and vanilla in an electric mixer on full speed for 12–15 minutes or until thick, pale and triple the original volume. Sift the flour and baking powder twice then sift half the flour mixture over the egg mixture and fold in gently using a large metal spoon. Repeat with the rest of the flour the add the cooled butter and fold to combine. Divide the batter between the prepared moulds - filling them to 3/4 full - then bake for 12-15 minutes or until golden but springy to the touch (a skewer inserted into the middle of each cake should come out clean). Allow the Tinkies to cool slightly before removing from the foil moulds.
To make the filling, place the egg whites and salt in a large metal or glass bowl over a pot of gently simmering water and whisk until soft peaks form. Gradually add the caster sugar while whisking until the mixture is stiff and hot to the touch. Remove from the heat and whisk until cooled (preferably with an electrical mixer) then add the vanilla. With the mixer running, slowly and gradually add the butter in small blobs, whisking well in between, until a fluffy buttercream forms. Place the frosting in a piping bag fitted with a medium straight nozzle.
Fill the Tinkies by pressing the piping bag nozzle into the bottom of the cakes at three different points and releasing the frosting inside each cake.
Recipe reprinted with permission of Katelyn Williams.
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