Instructions

Cook brandy and jelly together in 10-inch non­stick skillet over medium heat until thick and ­syrupy, 2 to 3 minutes. Remove skillet from heat and place plums cut side down in syrup. Return skillet to medium heat and cook, shaking pan to prevent plums from sticking, until plums release their juices and liquid reduces to thick syrup, about 5 minutes. Let plums cool in skillet, about 20 minutes.
Adjust oven rack to middle position and heat oven to 350 degrees. Grease 9-inch springform pan, line bottom with parchment, and grease parchment.
Process granulated sugar and almonds together in food processor until nuts are finely ground, about 1 minute. Add flour blend, baking powder, salt, and xanthan gum and pulse to combine, about 5 pulses. Add butter and pulse until mixture resembles coarse sand, about 10 pulses. Add egg, yolk, vanilla, and almond extract and process until smooth, about 5 seconds, scraping down bowl if needed (batter will be very thick and heavy).
Scrape batter into prepared pan and smooth top. Stir plums to coat with syrup, then arrange wedges in two rings over top of cake. Bake until cake is golden brown, 40 to 50 minutes, rotating pan halfway through baking.
Run knife around edge of cake to loosen. Let cake cool in pan on wire rack for at least 30 minutes. Remove cake from pan, discard parchment, and transfer to serving platter. Dust with confectioners’ sugar and serve warm or at room temperature.