In a medium bowl, whisk together the sugar, cornstarch, cinnamon, and nutmeg to combine the dry spices evenly. Add the sliced peaches and 2 tablespoons of lemon juice, then gently toss until the peaches are well coated and the cornstarch is fully incorporated. Let this mixture sit for 5 minutes to allow the peaches to start releasing their juices—this creates a more cohesive filling. I prefer using bottled lemon juice for consistent acidity, which ensures the filling has the right balance every time.

While the peaches rest, preheat your oven to 375°F. In a large bowl, whisk together the flour, 2 tablespoons sugar, baking powder, baking soda, and salt. Add the cold butter cubes and use a pastry cutter, fork, or your fingertips to work the butter into the flour until the mixture resembles coarse breadcrumbs with some pea-sized butter pieces remaining. In a small bowl, whisk together the cream, 1/2 teaspoon vanilla extract, and 1/2 teaspoon lemon juice. Pour the cream mixture into the flour mixture and stir gently with a fork just until a shaggy dough forms—don't overmix, as this keeps the topping tender and flaky.

Divide the peach filling from Step 1 evenly among six mason jars or oven-safe jars, filling each about two-thirds full. Drop spoonfuls of the biscuit dough from Step 2 onto the peach filling in each jar, leaving it slightly rustic and uneven rather than smooth—this creates better texture contrast. Sprinkle a small amount of sugar crystals over each jar's topping if desired for added crunch and visual appeal. Arrange the jars on a large baking tray and bake at 375°F for 35 to 40 minutes, until the topping is golden brown and the fruit filling is bubbling slightly around the edges. I always watch them carefully during the last 5 minutes to ensure the tops brown evenly without burning.

Remove the jars from the oven and let them cool for 5 to 10 minutes until the jars are safe to handle but still warm. Serve the cobblers warm or at room temperature, either in the jars for a charming presentation or spooned into bowls.