Easy coconut cake

Cake

• 250 g unsalted butter, cut into pieces, softened, plus extra for greasing
• 1 piece lemon zest (1 x 4 cm), no white pith
• 100 g raw sugar
• 250 g desiccated coconut
• 6 eggs
• 100 g gluten free cornflour
• 2 tsp natural vanilla extract
• 1 tbsp gluten free baking powder (see Tips)

Custard filling

• 40 g raw sugar
• 30 g gluten free cornflour
• 1 egg
• 250 g full cream milk
• 4 tbsp rum (optional)
• pure icing sugar, for dusting