In a large bowl whisk together brown sugar, cornstarch, and cinnamon. Add plums, lemon juice, and butter. Toss mixture well and spoon into a shallow 3-quart baking dish.
Preheat oven to 375 degrees.
In a food processor pulse together granulated sugar, flour, baking powder, salt, and 1/2 cup almonds until almonds are ground finely. Add the egg and pulse until blended. Spoon flour mixture over plum mixture, pulling some plum wedges up for presentation. Sprinkle remaining 1/4 cup almonds over cobbler.
Bake cobbler in the middle of oven 45 minutes, or until golden and bubbling, and cool on rack. Serve cobbler warm or at room temperature.
Recipe courtesy of Gourmet Magazine