Step 1
Position rack in centre of oven and preheat oven to 175°C (155°C fan-forced). Generously brush a 22cm x 12cm loaf pan with softened butter and line the base with baking paper.
Step 2
In a medium saucepan over high heat, bring raisins and ½ cup (125ml) water to boil. Reduce heat to medium. Simmer for 4 mins or until raisins are tender and liquid has evaporated. Stir in bicarbonate of soda. Remove from heat. Cool.
Step 3
In a small bowl, stir flour, baking powder, cinnamon and ¼ tsp salt to blend. In a large bowl, using an electric hand mixer, beat 90g butter, sugar and 1½ tsp orange zest on medium-high speed, scraping down side as needed, for 2 mins or until blended. Add eggs and vanilla and beat for 1 min or until batter is light and airy. Reduce speed to low. Add ¾ cup (185ml) orange juice in 2 batches, alternating with flour mixture. Beat on medium-high speed for 1 min (batter may appear split but this will not affect finished cake). Fold in raisins, carrots and walnuts.
Step 4
Pour batter into prepared pan. Wrap pan tightly with plastic wrap. Place in a 33cm x 22cm baking dish. Add enough boiling water to come halfway up sides of pan. Cover baking dish tightly with foil. Carefully transfer dish to oven. Bake for 1 hour 45 mins or until cake springs back when gently pressed and a toothpick inserted into centre comes out clean. Remove foil and plastic wrap. Transfer pan to a wire rack for 10 mins to cool. Turn onto a serving platter. Slice.
Step 5
To make mascarpone cream, in a medium bowl, using an electric hand mixer on medium speed, beat cream, mascarpone and sugar until soft peaks form. Serve with the cake.