Line a 1 1/2 quart glass or stainless bowl with plastic wrap, leaving enough excess hanging over the edge, and stick it in the freezer.
In a medium pot, combine the cherries, 1 cup of sugar, lemon juice, kirsch, and 3/4 cup of water. Simmer over medium-high heat until the juice from the cherries is released and the fruit is soft, about 20 minutes. Mix the cornstarch with 2 tablespoons of water to make a slurry and add it to the cherry mixture. Simmer, stirring, for another 2 minutes to thicken. Remove the cherry sauce from the heat, you should have about 4 cups. Put the cherry sauce in the freezer or in an ice bath to chill until cold.
Using a wire whisk, beat 2 cups of the heavy cream, the remaining 1/4 cup of sugar, and vanilla together until soft peaks form. Using a rubber spatula, fold the whipped cream into half of the cherry mixture (2 cups) to make a light mousse – don't overdo it, it's ok if there are streaks of cream in the filling. Gently fold in the pistachios. Take the plastic-lined bowl out of the freezer and spoon the cherry mousse into it, filling it all the way to the top, and spreading evenly around the rim. Freeze again for at least 8 hours, so the mousse sets up firm.
Heat the remaining 1 cup of cream and the chocolate in a pot over medium-low flame. Stir to melt the chocolate completely and smooth it out into the cream. Cool until warm to the touch, the chocolate should still be pourable.
Take the bowl of cherry mousse out of the freezer and invert it, bottom-side up, on a wire rack set over a sheet pan. Carefully peel off the plastic and pour the chocolate ganache over the bombe to cover it completely, allowing the excess to drip down into the sheet pan. Stick the chocolate cherry bombe back in the freezer to chill. Using a couple of flat spatulas, carefully remove the bombe from the rack and put in on a chilled platter. Cut into wedges; serve with the reserved cherry sauce.