Cake: Preheat oven to 350 degrees. Butter two 8-by-2-inch round cake pans. Line pans with parchment; butter parchment. Dust with flour, tapping out excess. In a food processor, finely grind pistachios. Remove and reserve 1/4 cup ground pistachios, then add flour, baking powder, baking soda, and salt to processor and pulse to combine.

Beat butter with granulated sugar on medium-high speed until light and fluffy, about 2 minutes. Add orange-flower water; beat to combine. Beat in eggs and yolks, one at a time, thoroughly combining after each addition and scraping down bowl as needed. Add pistachio mixture in three batches, alternating with sour cream and beginning and ending with pistachio mixture.

Divide batter evenly between cake pans; smooth tops with an offset spatula. Bake, rotating pans once, until tops spring back when lightly touched, 30 to 35 minutes. Transfer pans to a wire rack; let cool 10 minutes. Turn cakes out onto rack; remove parchment and let cool 1 hour. Wrap in plastic and refrigerate at least 1 hour and up to overnight.

Filling: Meanwhile, combine ricotta and cream in bowl of food processor; process until smooth. Add salt, vanilla, cinnamon, and confectioners' sugar; process to combine. Transfer mixture to a bowl and stir in chopped chocolate and orange peel. Refrigerate in an airtight container at least 1 hour and up to 2 days.

Cut each cake horizontally into 2 layers. Stack on a cardboard cake round or a plate; brush edges with melted chocolate, then pat some of reserved ground pistachios onto chocolate. Separate, then refrigerate in a single layer until set, 10 minutes. Place one cake layer on a cake stand, bottom-side down; spread 1 1/2 cups filling evenly over top, then place second layer on top. Repeat with remaining filling and cakes, finishing with a cake layer, bottom-side up. Refrigerate at least 1 hour and up to overnight. Sprinkle with confectioners' sugar and remaining reserved ground pistachios.