Here is the full recipe for those who want to give this a try!
250g beetroot, cooked and peeled
200g dark chocolate, chopped
4 Tbsp hot espresso
135g plain flour
1 Tsp baking powder
3 Tbsp cocoa powder
5 eggs, yolks and whites separate
190g caster sugar
Preheat the oven to 180°C/160°C fan.
Blend the beetroots.
Melt the butter.
Melt the chocolate in the butter, don't stir.
Stir together the butter and chocolate until well combined. Leave it to cool for a few minutes.
Sift the flour, baking powder and cocoa. Set aside.
Pour the chocolate into a bigger bowl and quickly stir in yolks.
Fold in the beetroot.
In a separate bowl beat the egg whites until stiff. Fold in the sugar.
Fold in the egg whites mixture into the chocolate one. Mix until well combined, but do not overmix.
Add in the espresso and stir.
Fold in the flour mixture.
Pour the batter into the pan and place in the oven. Lower the heat to 160°C/140°C fan.
Bake for around 40 minutes, the outer part should be firm, but the middle still wobbly Leave it to cool.