Toss 4 lbs sour cherries, pitted, with16 oz granulated sugar and allow to macerate for 30 minutes. After 30 minutes drain the cherries, reserving the juice. Transfer the cherries to a large bowl and set aside.
Preheat the oven to 375 °F. Place a 12" cast iron skillet into the oven to preheat (if using a 13"x9" baking pan you don't need to preheat the pan).
Whisk a 1/2 cup of the cherry juice with 1 ½ oz corn starch until smooth.
Place the remaining juice and ¼ teaspoon table salt in a saucepan over high heat. Bring the juice to a boil. Reduce the heat to medium low. Whisk the cornstarch mixture into the boiling juice in a steady stream. Cook the mixture, stirring constantly, until it returns to a boil and thickens.
Remove the thickened juice from the heat and immediately pour it over the pitted cherries. Toss to combine. Set the bowl aside while you make the topping.
Whisk together the 5 oz all-purpose flour, 3 ½ oz cake flour, ½ teaspoon table salt, 2 teaspoons baking powder and 2 oz granulated sugar. Toss 4 oz unsalted butter slices into the flour. Use your fingers to work the butter into the flour until the pieces are no larger than a pea.
Whisk1 large egg, ½ teaspoon almond extract with 8 oz heavy cream. Pour the cream into flour mixture. Toss the mixture with a spoon or spatula until it begins for form a wet dough.
Pour the cherries into the preheated 12" cast iron skillet or a 9"x13" baking pan. Use an ice cream scoop or large spoon to drop dollops of batter over the cherries. Generously sprinkle the top of the biscuits with granulated sugar.
Slide the pan into the oven. Place a sheet of foil on the shelf beneath the cobbler in the oven to catch any cherry juice boil over.
Bake until the topping is golden brown and baked in the middle and the juices are bubbling, about 35-40 minutes.
Serve warm or room temperature.