2 medium Rome apples
2 tablespoons fresh lemon juice
2 tablespoons packed dark brown sugar
1/4 cup water
1/4 cup old-fashioned rolled oats
1/8 teaspoon ground cinnamon
1/8 teaspoon salt
2 teaspoons cold unsalted butter, cut into bits
Special equipment: 4 (1/3-cup) round shallow ceramic baking dishes
Put oven rack in middle position and preheat oven to 375?F.
Peel and halve apples, then core (preferably with a melon-ball cutter).
Cut apples into thin slices and toss with lemon juice and 1 tablespoon brown sugar in a bowl.
Divide apples among baking dishes, overlapping slices, and sprinkle each serving with 1 tablespoon water.
Bake on a baking sheet until apples are crisp-tender, about 20 minutes.
Meanwhile, stir together oats, cinnamon, salt, and remaining tablespoon brown sugar in a bowl until combined. Rub butter into oat mixture for topping until evenly distributed.
Sprinkle topping over apples and bake until topping is golden, 25 to 30 minutes more.
Transfer dishes to a rack to cool at least 10 minutes. Serve warm or at room temperature.