Make the frangipane: In a food processor, pulse blanched almond flour, granulated sugar, and butter in a stand mixer fitted with the paddle attachment on medium speed until light and fluffy, about 2 minutes. Add egg, all-purpose flour, and salt. Beat until combined, about 2 minutes. Set aside.

Make the cake: Preheat oven to 350°F. In a 9- x 9-inch baking pan with butter. Line with parchment paper, leaving a 2-inch overhang on 2 long sides. Grease parchment with butter. Set aside.

Whisk together flour, salt, baking powder, and baking soda in a medium bowl. Set aside.

Beat granulated sugar and butter in a stand mixer fitted with the paddle attachment on medium-high speed until light and fluffy, about 3 minutes. Reduce mixer speed to medium; add eggs and egg yolk, 1 at a time, beating well after each addition. Beat in vanilla. With mixer running on low speed, add flour mixture alternately with sour cream in 3 additions, beginning and ending with flour mixture, until well incorporated after each addition. (Batter will be very thick.)

Transfer batter to prepared baking pan, and spread in an even layer using an offset spatula. Dollop preserves evenly on top; spread to cover as much of batter surface as possible. Dollop frangipane over preserves using a tablespoon. Drag a skewer through frangipane and preserves, without disturbing the cake batter layer beneath, to create a swirled pattern. Sprinkle evenly with almonds.

Bake in preheated oven until a wooden pick inserted in center of cake comes out clean, about 35 minutes. Let cool in pan on a wire rack 20 minutes. Using parchment as handles, remove cake from rack, let cool completely on wire baking pan, 45 minutes to 1 hour. Dust with powdered sugar, if desired.