Preheat oven to 300F degrees. Grease a deep 8" round cake pan and line the base with parchment paper.
Half-fill a saucepan with water and bring to a boil. Remove from heat. Place the chocolate in a heatproof bowl and place the bowl over the pan, making sure the bottom of the bowl isn't touching the water. Stir the chocolate occasionally until completely melted.
Put the eggs in a heatproof bowl. Add the Frangelico. Place the bowl over a pan of just simering water on low heat, making sure the bottom of the bowl doesn't touch the water. Using an electric mixer, beat the mixture on high for 7 minutes, or until light and foamy. Remove from heat.
Use a metal spoon to quickly and lightly fold the chocolate and nuts into the egg mixture until just combined. Fold in the cream and pour into the cake pan.
Place the cake pan in a shallow roasting pan. Pour enough hot water into the roasting pan to come halfway up the side of the cake pan.
Bake for 1 hour, or until just set.
Remove cake pan from the roasting pan and allow to cool to room temperature.
Cover with plastic wrap and refrigerate overnight.
Invert the cake onto a plate and remove the parchment paper. Cut cake into slices. Lightly dust each slice with confectioners sugar and serve with thick cream, if desired.