Preheat your oven to 400 degrees F and grase a casserole dish well.
In a large bowl, combine the flour, sugar, baking powder, salt, and shredded butter. With your hands (or pastry blender) combine the butter and flour mixture until the pieces are pea sized and crumbly.
For the fruit mixture, combine the cherries, rhubarb, lemon zest, lemon juice, sugar, cinnamon, and corn starch. Stir it well and cook it over medium heat until it’s thick and bubbly. Transfer the mixture to the greased casserole dish.
In a small bowl, whisk together egg and milk, then add the egg mixture to the flour mixture and stir until it’s just combined.
Loosely form the dough into 4-6 biscuits and then drop them onto the fruit mixture. Top with extra granulated sugar if desired.
Bake the cobbler for 20-25 minutes, or until the biscuits are golden brown. Serve with plenty of vanilla ice cream and enjoy!