Preheat the oven to 400 degrees F (200 degrees C). Coat a baking dish with cooking spray.

Halve and pit the plums, then slice or quarter, depending on size. Place fruit in a single layer in a baking dish. Drizzle lemon juice over fruit, add 2 tablespoons sugar, cornstarch, and vanilla extract, and toss to coat; set aside.

Add flour, 2 tablespoons sugar, baking powder, and salt to a bowl, and mix until well combined. Cut butter into small cubes, and mash into the flour mixture using a fork or pastry cutter until crumbly. Stir in boiling water to form a dough. Use your fingers or drop small spoonfuls of the dough on top of the plums.

Brown top of meringue with a kitchen torch, 2 to 3 minutes. (To store, insert toothpicks into meringue halfway up toothpick; loosely drape plastic wrap over toothpicks to cover. Chill up to 24 hours.)

Bake until a toothpick inserted into cobbler dough comes out clean and top is lightly browned, 25 to 30 minutes.