For The Pastry:
6 tablespoons unsalted butter
¾ cup water
¼ teaspoon salt
¾ cup all purpose flour
For The Cherries:
1-cup dark cherries, stones removed and sliced
¼ cup kirsch liquor
½ cup granulated sugar
Toss together and set in fridge for an hour before using.
For The Custard Filling:
1-cup caster sugar
5 egg yolks
2/3 cup sifted all-purpose flour
2 cups boiling milk
1 ½ tablespoons vanilla or 3 tablespoons kirsch
For the Ganache:
2 1/3 cups semi-sweet or bittersweet chocolate
1-cup heavy cream
2 tablespoons corn syrup
1-tablespoon vanilla or liquors
Preheat oven to 425 degrees F. Place rack in upper third of oven. Grease a baking sheet. Boil together butter water and salt in a heavy saucepan (such as enamel over cast iron) until butter is melted. Reduce hat to medium and add flour, cooking until it comes together in a ball (half a minute). Transfer to a larger bowl and cool a few minutes. Add eggs using an electric mixer, one at a time. Beat on high speed.
Using a pastry bag if you have one (otherwise use two spoons) make 6 long strips. Bake 15 minutes and then reduce heat to 400 degrees F. Poke a slit in the side of each and return to the oven. Bake another 15 minutes. Then bake another ten with the oven on but the door propped open. You may need to go as long as another ten minutes to dry the insides out adequately. You likely will never get them completely dry. This is fine; just use a sharp, thin knife to carefully pull out the rubbery insides after they cool a bit. It's simply the nature of larger choux pastry items.
Cool on a rack completely before frosting and filling.
Make the custard.
In a large bowl, break the eggs and slowly beat in the sugar, beating until pale yellow and eggs form a ribbon. Beat in the flour. Slowly add the boiling milk in a thin stream, beating as you go. Pour mixture into a heavy saucepan and using a wire whisk, bring to a boil over medium heat taking care to scrape the bottom as you go. Cook an additional two minutes following the boil being careful not to scorch it.
Remove from heat; beat in the butter and flavourings.
Make ganache by heating 2 tablespoons corn syrup with 1-cup heavy cream. When it begins to steam, pour over 2 1/3 cups chopped chocolate. Let stand five minutes, and then using a whisk, blend until smooth. Add any vanilla or other flavourings. You will have a good amount left over which can be hardened and used for truffles.
When pastry is cool, split and clean out the insides. With a spoon, cover tops with ganache. Return to refrigerator to set. Fill with custard and drained cherries. Replace tops and chill well before serving.