In a medium bowl, combine yeast, water and caster sugar. Cover and let stand 10 minutes, or until foamy. Add eggs, curd, vanilla, lemon zest and salt. Mix well. Stir in flour a little at a time until dough forms into a manageable ball. Turn out onto a lightly floured surface and knead for 5 to 10 minutes, adding flour as necessary, until dough is soft and pliable, but not sticky. Place dough in a large, lightly greased bowl. Cover and let rise in a warm place until doubled, about 1 hour.
Lightly grease a round 20cm cake tin. In a small bowl, toss fruit with icing sugar. Punch down dough in bowl, transfer to floured surface and knead in the fruit.
Form dough into a ball, place in prepared cake tin, cover loosely with a clean towel and let rise 30 minutes. (Loaf will rise above the tin sides.) Brush with melted butter, if desired.
Preheat oven to 180 C. Bake for 45 minutes, or until loaf is golden brown and a skewer inserted in the centre comes out clean.