Preheat oven to 350F (175C).

Butter a 10-inch diameter cake pan and line the bottom with parchment paper.

Butter the parchment paper and dust the pan with flour.

Melt semisweet chocolate in a double boiler over simmering water. Remove from heat.

Add unsalted butter 1 tablespoon at a time, mixing until melted and smooth.

Mix in sugar and grated orange peel.

Mix in eggs 1 at a time, then stir in egg yolk.

Add cake flour and ground ginger, then chopped toasted almonds and crystallized ginger. Stir to combine.

Transfer batter to prepared pan and bake for about 1 hour and 5 minutes, or until just springy to the touch.

Cool cake in pan on a rack for 15 minutes, then turn out onto rack, remove paper, and cool completely.

For the glaze, scald whipping cream with Grand Marnier liqueur in a heavy small saucepan.

Remove from heat and add minced semisweet chocolate, mixing until smooth.

Cool chocolate glaze until thick enough to spread.

Arrange cake flat side up on a rack and spread glaze evenly over top and sides.

Refrigerate until glaze is firm, about 30 minutes.

Transfer cake to serving platter.

Cut orange slices in half. Twist three halves and place in the center of cake.

Arrange remaining orange slices around the edge of the platter and serve.