In a large bowl, fold the pears (3 pounds), white sugars (1/2 cup), cinnamon (1/2 teaspoon), nutmeg (1/4 teaspoon), vanilla extract (1/2 teaspoon), lemon juice (1 teaspoon), and cornstarch (2 teaspoons) until all ingredients are well combined.
Pour fruit mixture into a 9X13-inch baking dish.
Place in preheated oven and bake for 10 minutes.
While the pears are in the oven, mix together all the cake topping ingredients, except the boiling water, to a medium bowl.
Use a pastry blender to cut the butter into the dry ingredients until the mixture looks like coarse meal.
Pour in the boiling water (1/2 cup) and stir just until the mixture comes together and is just mixed through.
After the pears have baked the 10 minutes, pull them from the oven and drop large spoonfuls of the dough topping over the pears.
Evenly sprinkle the top of the dough with the 3 tablespoons of sugar.
Place the baking dish on a cookie sheet, in case the cobbler bubbles over and drips, and bake for 30-35 minutes or until the topping is golden and baked through and the pears are tender.