Preheat oven to 325°F. Line a 9-inch round cake pan with parchment paper, and spray with baking spray with flour.

Arrange clementine sections in an even layer in prepared pan.

In a small bowl, whisk together ¾ cup (75 grams) pastry flour, baking powder, and salt. In the work bowl of a food processor, pulse together sugar, zest, almond paste, and remaining ¼ cup (25 grams) pastry flour until well combined, 3 to 4 minutes. With processor running, add butter, 1 tablespoon (14 grams) at a time. Add vanilla bean seeds. Process until mixture is smooth, 3 to 4 minutes. With processor running, add eggs, one at a time. Gradually add flour mixture, pulsing until combined. Pour batter over clementines.

Bake until golden brown and a wooden pick inserted in center comes out clean, 50 minutes to 1 hour. Let cool in pan for 5 minutes. Run a knife around edges of pan to loosen before inverting onto a wire rack to let cool completely. To serve, invert cake onto a serving platter. Garnish with Candied Clementines, if desired.