Heat your oven to 160°C fan. Chop the butter into small cubes and add to a mixing bowl. Finely chop the chocolate and add to the bowl.
Butter a 20cm x 30cm roasting tin, then add a tbsp of cocoa powder and shake around the tin so the cocoa dusts the surface. Tip out any excess.
Add 5cm of water to the base of a small saucepan, bring to the boil then turn down the heat to a simmer. Place the bowl of chocolate and butter on top of the saucepan and gently melt, stirring regularly. Stir in the cocoa powder, vanilla essence, and a pinch of salt. Set aside.
Add the eggs and sugar to a separate bowl and use an electric whisk to whip the until the mixture is light and fluffy. Fold in the chocolate mixture, using a spatula to mix the two together. Try not to knock out too much of the air you’ve whipped into the eggs!
Use a sieve to dust the flour over the top of the mix. Fold the flour through the mix, making sure there are no white streaks of flour and the mix is homogenous. Tip into a prepared dish. Give it a wiggle to level out the mixture.
Bake for 18-20 mins, until it’s set around the edges with a decent wobble in the middle. Dust with cocoa powder and finish with a pinch of sea salt. Serve straight away with ice cream.
