Carrot Cake With Lime Mascarpone Icing

Name: Carrot Cake With Lime Mascarpone Icing
Ingredients: 1 1/4 cups unsalted butter, room temperature, plus more for pan; 2 cups light-brown sugar; 5 large eggs, separated; Zest and juice of 1 orange; 1 slightly heaped teaspoon baking powder; 1 heaped teaspoon ground cinnamon; Pinch of ground cloves; Pinch of ground nutmeg; 1/2 teaspoon ground ginger; 1 cup ground almonds; 4 ounces shelled walnuts, chopped, plus more for garnish; 1 1/2 cups self-rising flour, sifted; 10 ounces carrots, peeled and coarsely grated; Sea salt; 4 ounces mascarpone cheese; 8 ounces cream cheese, room temperature; 1 scant cup confectioners' sugar, sifted; Zest and juice of two limes