preparing the zabaglione filling
Beat egg yolks in a heat proof bowl until fluffy. Beat in sugar and orange juice.
Whisk over a pan of simmering water, until the cream thickens.
assembling the cake
Turn the panettone upside down and cut the bottom about 3/4-inch (2 cm) from the edge.
Remove the panettone bottom.
Cut away the excess panettone and place in a bowl. Reserve the panettone bottom.
Carve the panettone removing the core portion and leaving the wall intact. Place the panettone crumbs in the bowl.
Mince the panettone crumbles in small pieces.
Add the zabaglione. Combine the panettone crumbles and the zabaione.
Soak the inside walls of the panettone cavity with the Marsala wine.
Fill the cavity with the zabaglione/ panettone mix.
Place the panettone disk back on the opening to close the bottom.
Turn the panettone back upright.
preparing the chocolate glaze
Mix together in a saucepan the water, corn syrup, and sugar.
Bring to a boil, remove from the stove, and add the diced chocolate. Stir occasionally to melt the chocolate.
Pour the glaze on the panettone while the chocolate is still hot.
Leave the panettone aside to set at room temperature for about 2 hours.