To make the Cherry Sauce (This can be done in advance):
Measure 1 cup sugar, then remove 1 tablespoon and transfer to a small saucepan. Set remaining sugar aside for the cake.
Pour one tablespoon of cherry juice from the can into a small bowl; whisk in cornstarch and set aside.
Then pour the remaining juice from the can into a small saucepan, holding back the cherries. Transfer the cherries to a cutting board and halve or quarter if large. Add cherries to the saucepan and bring to a boil. Reduce heat and simmer, stirring occasionally, until cherries have begun to break down and sauce has reduced slightly. Stir in cornstarch and juice mixture and boil until sauce thickens, about 1 minute. Stir in orange zest and let cool to room temperature.
For the cake:
Preheat the oven to 350 degrees. Butter an 8-inch round cake pan. Line the bottom with a circle of parchment paper; then butter parchment and coat lightly with flour, tapping to remove the excess.
Sift flour, cocoa powder, ginger, and baking soda into a large bowl; whisk in salt.
With an electric mixer, beat butter and reserved sugar (1 cup minus 1 tablespoon) on high speed until fluffy, about 2 minutes. Add eggs, one and a time, beating to combine after each and scraping down the bowl if necessary. Mix in the sour cream. With mixer on low, add the flour mixture in two parts. Fold in ½ of the cooled cherry sauce; reserve the remaining sauce for the topping.
Pour batter into the prepared pan; smooth the top. Bake until a toothpick or wooden skewer inserted in the center comes out clean, 35-40 minutes. Transfer to a wire rack and let cool 10 minutes. Invert cake onto a wire rack to cool completely. Transfer cake to a serving platter.
For the topping:
Beat heavy cream until soft peaks form; gradually sprinkle in sugar and beat until stiff peaks form. Fold in sour cream.
Scrape cream onto cake and smooth with a spatula, leaving a 1-inch border. Top with reserved cherry sauce before slicing and serving.