Line a 900g/2lb loaf tin with parchment paper or pre-made loaf tin liner

Preheat the oven to 170ºC/150ºC fan/325ºF/Gas mark 3

Using a stand mixer, cream the butter and sugar

In a small measuring jug, beat the eggs with the vanilla extract

In a separate mixing bowl, sift together the plain and self-raising flour

With the mixer on a low speed, slowly pour in the beaten eggs in three stages, alternating with the addition of a tablespoon of the flour (to stop the mixture curdling)

Add the remaining flour, cacao nibs and lemon zest

Mix in the lemon juice

Pour the batter into the lined loaf tin and level using a spatula or back of a spoon

Sprinkle the top with the granulated sugar

Bake for 1 hour or until a skewer inserted into the centre comes away clean

Allow to cool in its tin for ½ hour before turning out on to a wire rack