1) Preheat the oven to 180°C/ gas mark 4. Grease a 23-cm cake pan and line the bottom with parchment paper.
2) Combine the 20 amaretti cookies and the chocolate in a food processor. Run the machine until the mixture is very finely minced. Set aside.
3) Using an electric mixer and a large bowl, cream together the butter and sugar until pale yellow, about 2 minutes. Add the egg yolks 1 at a time, incorporating each yolk before adding the next. Once all the eggs are added continue to cream the mixture together until light and fluffy, about 4 more minutes. Add the orange liqueur. With the machine on low, add the flour and the chocolate amaretti mixture. Mix well after each addition.
4) In medium bowl whip the egg whites using an electric mixer until stiff peaks form, about 3 minutes. Add 1/3 of the whipped egg whites into the cake mixture until well combined. Gently fold in the remaining whipped egg whites. Pour the batter into the prepared cake pan. Bake until a toothpick comes out clean, about 45-50 minutes.
5) Let the cake cool in the pan on a wire rack for 10 minutes. Turn the cake out onto a platter and continue to cool to room temperature. Top with the orange marmalade in an even layer. Sprinkle the remaining crushed amaretti cookies over the top of the cake. Slice and serve.