(slightly adapted from: Poires au Chocolat)
3 tbsp cocoa powder
2.5 tbsp boiling water
1 tsp vanila extract
145g plain flour
1.5 tsp baking powder
130g soft butter
140g caster sugar
Preheat oven to 180°C. Line a 20cm diameter springform pan with parchment paper.
Mix together the cocoa powder and boiling water and let cool. When it is cool, whisk in the eggs and vanilla extract and put aside. Sift the flour and baking powder into another bowl. Cream the butter, ricotta and sugar together with a hand mixer at medium speed until it is light and fluffy (3-4 minutes). Add zest of one lime and the juice of half a lime. Add 1/3 of the chocolate mixture, beat to combine, then add a 1/3 of the flour. Repeat this until all is combined.
Pour the batter into the prepared springform pan and bake for about 30-40 minutes. A skewer should come out clean. Let cool for 5 minutes before turning out.
For the icing mix together about 100g icing sugar with as much lime juice as you need until you have a creamy mixture that you can spread over your cake. Scatter grated zest of one lime on your cake.