Sweet Potato Doughnuts

Name: Sweet Potato Doughnuts
Prep time: 20 min
Cook time: 1 h
Total time: 1 h
Yield: 12 pieces
Ingredients: 150 g sweet potatoes; 150 g water; 40 g olive oil; 120 g granulated sugar; 200 g whole milk; 1 large egg; 2 tsp vanilla extract; 200 g plain flour; 1 ½ tsp baking powder; 1 ½ tsp ground cinnamon; ½ tsp ground ginger; ¼ tsp ground nutmeg; 1 pinch fine sea salt; 30 g pistachio nuts, unsalted, shelled; 4 Tbsp icing sugar; 2 tsp water