Roast sweet potato whole at 200°C (400°F) for 45 to 50 minutes until completely soft. Scoop flesh, mash until completely smooth, measure 1 cup (245g), and cool to room temperature.

Preheat oven to 175°C (350°F). Line a 20x20cm baking pan with parchment paper with overhang on two sides.

Place chopped chocolate and butter in a heatproof bowl over a saucepan of barely simmering water. Stir until melted and smooth. Remove from heat and cool 5 minutes.

Stir sugar into the melted chocolate until fully combined. Add eggs one at a time, stirring well after each. Stir in vanilla.

Add cooled sweet potato mash and stir firmly until no orange streaks remain and the batter is uniform dark chocolate in color.

Sift in cocoa powder, flour, salt, and baking powder. Fold with a rubber spatula until just combined with no dry pockets. Do not overmix.

Pour batter into the lined pan and spread evenly. Scatter flaky sea salt over the top if using. Bake 22 to 25 minutes until edges are set and matte and center is still slightly glossy. A toothpick 2cm from the edge should come out with moist crumbs.

Cool in pan on a wire rack for minimum 20 minutes before lifting out. For cleanest cuts, refrigerate 30 minutes after cooling, then use a warm dry knife between each cut.