Preparation time 45 minutes (plus refrigeration time). Cooking time 25 minutes.
1. Preheat oven to moderate. Grease two deep 19cm-square cake pans; line bases with baking paper.
2. Beat eggs in medium bowl with electric mixer about 10 minutes or until thick and creamy. Add 1 cup of the sugar, 1 tablespoon at a time, beating until sugar dissolves between additions. Gently fold in triple-sifted flours, then ¼ cup of the boiling water. Divide mixture evenly between prepared pans; bake, uncovered in moderate oven about 25 minutes. Turn cakes immediately onto wire racks to cool.
3. Meanwhile, combine remaining boiling water, coffee and ½ cup of the marsala in small bowl, cool.
4. Beat egg yolks and remaining sugar is small bowl with electric mixer until thick and creamy. Add remaining marsala and mascarpone; beat until combined.
5. Line deep 19cm-square cake pan with plastic wrap. Split cooled cakes in half horizontally, place one layer of cake in pan, brush with 1/3 cup of the coffee mixture. Spread with 1 cup of the mascarpone mixture, sprinkle with 1 tablespoon of the grated chocolate. Repeat layering, finishing with layer of cake, cover; refrigerate 3 hours or overnight.
6. Beat cream in small bowl with electric mixer until soft peaks form. Turn cake onto serving plate; spread top and sides with cream. Using vegetable peeler, make chocolate curls from extra chocolate, sprinkle over cake.