Preheat your oven to 350°F (175°C). Grease a 9-inch round cake pan and line the bottom with parchment paper.

Melt 150g of the dark chocolate and all the butter together. You can do this in a heatproof bowl set over a pan of simmering water or in the microwave in 30-second bursts, stirring until smooth.

In a large mixing bowl, whisk the eggs and granulated sugar together until the mixture is pale and slightly thickened.

Pour the melted chocolate and butter mixture into the egg mixture and whisk until fully combined.

Sift the flour, cocoa powder, and baking powder into the wet ingredients. Gently fold the dry ingredients in using a spatula.

Stir in the orange zest, fresh orange juice, and chopped crystallized ginger until evenly distributed throughout the batter.

Pour the batter into the prepared cake pan and bake for 45-50 minutes, or until a skewer inserted into the center comes out mostly clean with just a few moist crumbs.

Allow the cake to cool completely in the pan before transferring it to a serving plate.

To make the ganache, heat the heavy cream in a small saucepan until it just begins to simmer. Place the remaining 50g of chocolate in a small bowl.

Pour the hot cream over the chocolate. Let it sit for 2 minutes, then stir gently until glossy and smooth.

Pour the ganache over the cooled cake, smoothing it out with a spoon or spatula. Let it set for 15 minutes before slicing.