Duck with mango purée and sweet potato mash

Name: Duck with mango purée and sweet potato mash
Ingredients: 1 tbsp soy sauce; 1 tsp ground ginger; 1 tsp garlic powder; pinch ground cumin; 1 fresh thyme sprig; pinch ground cinnamon; pinch dried red chilli flakes; pinch freshly ground black pepper; 2 duck breasts, skin on; pinch salt; 2 sweet potatoes; pinch ground ginger; 2 tbsp crème fraîche; 1 ripe mangoes, peeled, stone removed and flesh roughly chopped; 1–2 tbsp orange juice or water; dash rum (optional); 1 tbsp vegetable oil; 1 mango, peeled, stone removed and flesh chopped; 50g/1¾oz kale