Combine cocoa powder with boiling water and mix it with chocolate melt, butter, egg yolk, sugar. zest and almond meal in a large bowl.
Using electric blender, beat egg white until soft peaks form. Gently fold into the chocolate mixture in two batches.
Pour the mixture in the greased spring form tin of 20 cm and bake it in a preheated oven of 180 C for 45 minutes or more until firm.
Cool the cake and top it with the candied orange slice and drizzle it with the syrup.
Candied Orange 1/2 cups water 1/2 cup castor sugar[br]navel orange, sliced 1/4 inch thick[br]In a pan, combine the water and sugar and boil it. Add the orange slices and cook over a moderate heat, turning them occasionally, until the liquid is reduced to a thin syrup and the orange slices are translucent, about 20 minutes. Reduce the heat to moderately low and simmer until the syrup is thick and the slices are tender but still intact, turning occasionally, about 10 minutes. Transfer the orange slices to a rack to cool. Reserve the syrup and use it while serving the cake..