Preheat the oven to 180C/356F and lightly grease your bundt pan with butter.
Using the double boiler method, melt the chocolate and butter over a low-medium heat. Once they have melted, sieve in the caster sugar, cocoa powder and almond meal, all at the same time. Sieving the cocoa in with other ingredients discourages it from clumping together, meaning a smoother batter with less cocoa chunks.
Once the sugar granules have dissolved, take the mixture off the heat (be careful of the steam when removing the metal bowl from the saucepan) and add the coffee, rum, vanilla bean paste and sea salt. The sea salt and coffee work wonders in deepening the coffee flavour – I don’t recommend omitting them.
In a clean bowl, beat the eggs on a high speed, until they are fluffy and pale in colour.
Transfer the chocolate mixture to a large clean bowl. Use a spatula to gently fold a quarter or so of the fluffy egg mixture into the chocolate mixture at a time. The aim is to fully incorporate the egg mixture, while still retaining the air bubbles it provides. Slow and steady.
Once the mixture is fully incorporated, place the greased bundt pan on a flat tray, and divide the chocolate mixture between the moulds. Transfer to the oven for 15 minutes.