Preheat oven to 325°F (170°C).

In the bowl of a stand mixer fitted with the paddle attachment, beat granulated sugar, brown sugar, crème fraîche, cream, melted butter, egg, egg yolk, lemon zest, and extracts at medium speed until well combined, about 2 minutes, stopping to scrape sides of bowl.

In a large bowl, whisk together flours, baking powder, and salt. With mixer on low speed, gradually add flour mixture to sugar mixture, beating just until combined and stopping to scrape sides of bowl.

Spray a 9-inch springform pan with baking spray with flour. Line bottom of pan with parchment paper. Reserve ¾ cup batter. Spoon remaining batter into prepared pan, spreading into an even layer with a small offset spatula. Spoon Lemon Curd, 1 tablespoon (16 grams) at a time, onto batter in pan. Spoon reserved batter between curd dollops. Using the tip of a sharp knife, swirl curd into batter, being careful not to overmix.

Bake until a wooden pick inserted in center comes out clean, 40 to 50 minutes. Sprinkle edges with almonds. Let cool in pan on a wire rack for 10 minutes. Carefully remove sides of pan; let cake cool completely on pan base on wire rack. Remove pan base, and discard parchment. Just before serving, garnish with confectioners’ sugar, if desired.

In a medium saucepan, whisk together sugar, eggs, lemon zest, cornstarch, and salt until smooth. Add lemon juice, whisking until smooth. Cook over medium-low heat, stirring constantly, until mixture is bubbling, thickened, holds shape of whisk, and registers 170°F (76°C) on an instant-read thermometer, about 7 minutes.

Strain mixture through a fine-mesh sieve into a medium heatproof bowl. Add butter, 1 cube at a time, stirring until combined and mixture is smooth after each addition. Cover with a piece of plastic wrap, pressing wrap directly onto surface of curd to prevent a skin from forming. Let cool completely. Refrigerate in an airtight container for up to 1 week.