Preheat oven to 350°F/175 C. Line an 8”x8”/20cm x 20cm baking pan with parchment.

Beat eggs and sugar together until pale and ribbons form.

Add in tahini and 4 tbsp/60ml melted butter. Beat until smooth.

Fold in flour, baking powder, and salt.

Separate out 1/3 of batter into a smaller bowl. Add melted chocolate and remaining butter. Stir until smooth.

In the larger portion, add the orange zest and stir to evenly distribute.

Place alternating globs of mixtures in the lined baking pan, layering slightly. Swirl the mixtures together with a knife.

Place a few chopped pieces of orange on top of the batter, pressing them in slightly. Do not cover the batter as the orange will release moisture.

Sprinkle sesame seeds over the top.

Bake for 25-30 minutes, until the edges of the orange mix are slightly browned and a skewer inserted comes out with a few crumbs.

Allow to cool completely before cutting.