Start the chocolate batter: melt the chocolate and butter together until smooth, either in a double boiler or using short, low power bursts in the microwave, stirring in between to ensure it doesn’t burn. Set aside to cool slightly while you start the ricotta filling.

Start the ricotta filling: put the ricotta, butter and vanilla into the bowl of a stand mixer and mix on low speed until it’s well combined (you aren’t looking for super light and fluffy here, so don’t let it go too long). Add the sugar and mix until it’s not grainy anymore, then add the eggs one by one, mixing well after each addition. It will probably look curdled by this stage, but don’t worry. Remove the bowl from the mixer and gently fold in the flour. Scrape into another bowl, set it aside and rinse your mixer bowl so you can return to the chocolate batter.

To finish the chocolate batter: put the eggs and sugar into the mixer bowl and beat on medium speed until they’re thickened and creamy. Add the melted chocolate/butter and mix on low until it’s just incorporated. Remove the bowl from the mixer and gently fold in the flour and salt. It will be fairly stiff - don’t overmix here or it will become thick and tough.

Put two thirds of the chocolate batter into the base of the prepared tin and spread it out with the back of a spoon. Put all the ricotta filling on top of this, spreading it right to the edges. Dollop spoonfuls of the remaining chocolate batter on top, very gently pressing them down so they are fairly level with the ricotta filling. Take a butter knife and gently drag it through the chocolate and ricotta mixtures to marble them together a bit.

Bake the cake until it tests clean with a skewer, approximately an hour and a half. Allow to cool for an hour or two in the tin, then turn out onto a plate. You can serve it slightly warm or at room temperature, dusted with powdered sugar and decorated with Easter eggs if that’s your thing.