1 Preheat the oven to 200 degrees, or 180 degrees if using a fan oven. Grease a 23x10cm loaf tin with a little butter or oil and line with parchment paper.

2 Put the butter into a small saucepan over a medium heat for a minute or two, or until just melted. Alternatively, melt it in a microwave. Set aside to cool slightly.

3 Separate the eggs into two bowls, making sure you put the egg whites into a large spotlessly clean bowl. Add half the sugar (90g) to the egg yolks and whisk for about three to five minutes until pale and thickened slightly. Set aside.

4 Whisk the egg whites until frothy (use a stand mixer or electric beater if you wish), and gradually add the remaining sugar (90g), one tablespoon at a time, whisking well between each addition.

5 When all of the sugar has been added, continue to whisk until the egg whites have soft peaks. Set aside.

6 Pour the cooled melted butter into the egg yolks and sugar and whisk well to combine. Add the grated zest and juice from the grapefruit, then gently fold in the egg whites, a third at a time, taking care not to beat the air out.

7 When you can't see any remaining lumps of egg white, sift in the flour and add the poppy seeds, then gently fold the mix together until just combined.

8 Pour the batter into the prepared loaf tin and smooth the top. Bake the loaf in the preheated oven for 35-40 minutes until well risen and golden. There will be a few cracks in the cake and it will sink a little once it cools.

9 Remove from the oven and leave to cool for 10 minutes in the tin before removing from the tin and placing on a wire rack to cool completely.

10 For the drizzle, sift the icing sugar into a bowl and add the grapefruit juice, starting with a tablespoon and whisk well, adding a little more juice if needed, until you have a perfect drizzle consistency. Pour the drizzle over the cooled cake and serve.