Preheat oven to 375°F (190°C) and butter a 9x13-inch baking dish. Toss cherries with sugar, cornstarch, lemon juice, vanilla, and salt. Let sit 10 minutes, then pour into the prepared dish.
Whisk flour, sugar, baking powder, and salt in a bowl. Cut in cold butter until mixture resembles coarse crumbs. Stir in milk until just combined; dough will be slightly sticky.
Drop large spoonfuls of topping over the cherries, leaving small gaps for steam. Sprinkle coarse sugar on top if using. Bake 35–45 minutes until topping is golden and filling bubbles.
Cool 10–15 minutes to thicken slightly. Serve warm with vanilla ice cream or whipped cream.
Notes
If using frozen cherries, add about 5 minutes to the baking time.
For extra depth, replace 1/4 cup sugar with brown sugar or add 1/2 teaspoon cinnamon to the filling.
Assemble ahead and refrigerate up to 24 hours before baking, or freeze unbaked for up to 3 months.