Preheat the oven to 200°C/400°F/gas 6.Finely grate the zest of 3 of the oranges, then carefully remove the outer peel and slice across into wheel-shaped pieces, just under 1cm thick.Break up the dark chocolate and place in a small bowl and melt it over simmering water, stirring occasionally.Butter the inside of a deep 20cm metal tin or earthenware dish. Sift the flour into a clean bowl, add the almonds, half the sugar, a pinch of sea salt, the eggs, yolks, orange zest and milk. Whisk up until smooth, then add the rest of the butter to the melting chocolate.Scrape all the melted chocolate and butter into the batter mix and pour into the tin.Break up the white chocolate and poke little pieces into the batter, then bake in the oven for 16 to 20 minutes, or until firm around the edges but sticky and gooey in the middle. This doesn’t mean it’s undercooked ... it means it’s perfect! So be careful not to overcook it or it will just be like a boring sponge.While it’s cooking, bring the other half of the sugar to the boil on a medium heat with 6 tablespoons of water until you have a golden caramel. Remove from the heat, squeeze in the juice from the remaining oranges and stir it in to loosen the caramel slightly.Arrange the orange slices nicely on a plate, pour over the caramel and serve with the chocolate clafoutis and a bowl of crème fraîche or yoghurt (if using). Delicious.