Preheat your oven to 350°F (175°C). This ensures that your cobbler bakes evenly.

In a large mixing bowl, combine the sliced pears, granulated sugar, ground cinnamon, ground nutmeg, lemon juice, and cornstarch. Toss gently until the pears are well coated. This mixture will create a sweet and spiced filling.

Transfer the pear mixture to a greased 9-inch baking dish, spreading it evenly.

In another mixing bowl, whisk together the sifted flour, brown sugar, baking powder, and salt. This dry mix will provide the structure for the topping.

Add the melted butter, milk, and vanilla extract to the dry ingredients. Stir until just combined; do not overmix. This will keep the topping light and fluffy.

Pour the cobbler batter over the pear filling, spreading it gently to cover the fruit.

In a small bowl, combine the oats, flour, brown sugar, cold cubed butter, and ground cinnamon. Use your fingers or a pastry cutter to mix until the mixture resembles coarse crumbs. This will create a crunchy topping.

Sprinkle the crumble mixture evenly over the cobbler batter.

Place the baking dish in the preheated oven and bake for 35-40 minutes, or until the topping is golden brown and a toothpick inserted into the center comes out clean. This ensures that both the topping and filling are cooked through.

Once baked, remove from the oven and allow to cool for at least 10 minutes before serving. This resting time helps the filling set slightly.