5 1/2 cups heavy cream, preferably not ultrapasteurized
1 cup sugar
2 teaspoons unsweetened cocoa powder
1 tablespoon plus 1 teaspoon instant espresso powder
1/8 teaspoon freshly grated nutmeg
1 1/2 tablespoons finely chopped semisweet chocolate, plus chocolate shavings
6 ounces frozen sweet cherries (1 1/4 cups)
1 cup jarred sour cherries packed in juice
1/4 cup sugar
1 tablespoon fresh lemon juice
Pinch of freshly grated nutmeg
2 tablespoons water
Brush ten 1/2-cup ramekins with the melted butter and transfer to a large roasting pan. In a small bowl, whisk the gelatin into the milk and let stand until softened, about 5 minutes.
In a medium saucepan, combine the cream with the sugar and bring just to a boil over moderate heat. Remove from the heat and whisk in the cocoa, espresso powder and nutmeg. Whisk in the gelatin mixture until completely melted, then add the chopped chocolate and stir until melted. Strain the mixture into a large bowl; let cool to room temperature.
Pour the panna cotta mixture into the ramekins and refrigerate until firm, at least 4 hours or overnight.
Combine all the ingredients in a saucepan and simmer over moderate heat for 6 minutes. Transfer the sauce to a blender and puree. Strain and refrigerate.
Shortly before serving, dip the bottom of each ramekin in hot water for 30 seconds. Run a knife around each panna cotta and invert it onto a dessert plate. Lift off the ramekins. Spoon the cherry coulis around each panna cotta, garnish with chocolate shavings and serve.