1. Preheat the oven to 350°F (175°C). Grease and flour a large cake pan.

2. In a large bowl, whisk together the flour, sugar, and baking powder.

3. Add the softened butter and mix until the mixture resembles coarse crumbs.

4. In a separate bowl, whisk the eggs and saffron threads together until well combined.

5. Pour the egg mixture into the flour mixture and stir until just combined.

6. Melt the chocolate using a double boiler or microwave in 30-second intervals, stirring between each interval, until smooth. Allow to cool slightly.

7. Gently fold the melted chocolate into the batter until the mixture is smooth and uniform.

8. Fold in the grated orange zest until evenly distributed.

9. Pour the batter into the prepared cake pan and spread it out evenly.

10. Bake for 35 to 40 minutes, or until a toothpick inserted into the center of the cake comes out clean.

11. Allow the cake to cool in the pan for 10 minutes, then carefully remove it from the pan and transfer it to a wire rack to cool completely.