Although I've never tried baked plums, this recipe for nectarines is a favorite when they're in season:
Nectarines and Pistachios
4 tablespoons shelled pistachios
2 tablespoons unsalted butter
1/2 cup confectioners' sugar
2 drops (less than 1/8 teaspoon) almond extract (optional)
1/8 teaspoon salt
2 nectarines, halved and pitted
1/2 lemon
1/2 cup creme fraiche
1 tablespoon granulated sugar
Directions
Preheat oven to 400 degrees (F). Chop 3 tablespoons pistachios in a food processor until finely ground. Add butter, confectioners' sugar, almond extract, and salt. Process until combined.
Place nectarines, cut side up, on a baking sheet, and squeeze lemon over top. Place a generous tablespoon of pistachio mixture on each nectarine half. Chop remaining tablespoon pistachios, and sprinkle on top. Bake until fruit is tender and topping is crisp, 10 to 15 minutes. Let cool for 5 minutes. Transfer to 4 plates.
Whisk together creme fraiche and granulated sugar. Spoon over nectarines, and serve...