Step 1

Preheat oven to 160C. Line a 20cm square cake tin with baking paper.

Step 2

In a stand mixer, or using hand-held beaters, whisk egg whites to form stiff peaks.

Step 3

In a separate bowl, beat egg yolks and sugar until pale. Whisk in Milo, then add melted butter and whisk until smooth. Fold in flour, then add milk in a continuous flow while whisking until you have a very smooth, thin batter. Gently fold in egg whites until just combined.

Step 4

Pour into prepared tin and bake for 45 minutes. At this stage, check by gently shaking tin. If it is still wobbling, return to oven for a further 5-15 minutes, checking intermittently. If the top is becoming too brown, cover with foil.

Step 5

When the centre is set, remove from oven and allow to cool completely before cutting into squares.