Core the pears and cut them lengthwise into 1/2-inch thick slices. You don't need to peel them unless the skins are especially thick.

Place the sliced pears into a 2-quart baking dish. Drizzle the fresh lemon juice over the pears and gently toss to coat. In a separate bowl, whisk together the white sugar, cornstarch, and 1 teaspoon ground cinnamon. Add this mixture to the pears and toss well, ensuring the slices are evenly coated. I like to make sure every pear slice is evenly covered for a perfectly thickened filling.

In a medium bowl, combine the flour, 1/2 teaspoon ground cinnamon, packed brown sugar, and salt. Add the cold diced butter. Using a fork, pastry cutter, or your fingers, work the butter into the dry mixture until coarse, crumbly clumps form. Stir in the rolled oats and chopped walnuts to complete the topping.

Evenly sprinkle the crisp topping from Step 3 over the prepared pear mixture in the baking dish. Bake at 375°F (190°C) for about 40 minutes, or until the pears are tender and the topping is golden brown. I like to let the crisp cool for at least 10 minutes before serving to allow the juices to thicken slightly.

Serve the crisp warm, at room temperature, or chilled. Enjoy it plain, or with a scoop of vanilla ice cream or a dollop of whipped cream for an extra treat.