Preheat oven to 350℉. Grease an 8×8-inch pan or 2-quart baking dish well with butter and set aside.
In a large bowl, combine the peach slices, brown sugar, cornstarch, vanilla, lemon juice, lemon zest, ginger, cinnamon, and salt. Stir gently with a spatula or wooden spoon until the peaches are evenly coated with the spices and sugar.
Pour the peach mixture into the prepared pan and bake for 15 minutes.
While the peaches are baking, prepare the biscuit topping by mixing the flour, sugar, baking powder, baking soda and salt together in a large bowl. Cut the cold butter using a pastry cutter, food processor or two forks, cut the butter into the mixture until it resembles wet sand and the butter is about the size of a pea. Drizzle in the buttermilk and gently mix until the cookie dough is just combined – don’t over mix! If the peaches are not yet ready to be topped with the cobbler, refrigerate this mixture.
After 15 minutes of pre-baking, remove the peaches from the oven and spread the batter evenly over the peach filling.
In a small bowl, whisk together the egg and 1 tablespoon of buttermilk. Brush this mixture over the cobbler and then sprinkle with 1 to 2 tablespoons granulated sugar.
Return the peach marshmallows to the oven and bake for 37-42 minutes, or until lightly browned and the biscuit topping is cooked through and golden.
Serve warm with optional whipped cream ice cream.
