Preheat oven to 325°F (170°C).
For cake: Within the bowl of a stand mixer, whisk collectively granulated sugar and orange zest by hand till mixed and aromatic. Add butter; utilizing the paddle attachment, beat at medium velocity till gentle and fluffy, 4 to five minutes, stopping to scrape sides of bowl. Add eggs, separately, beating till mixed after every addition and stopping to scrape sides of bowl. Beat in vanilla.
In a medium bowl, whisk collectively flour, salt, and baking powder. In a small bowl, whisk collectively ricotta and orange juice. With mixer on low velocity, add flour combination to butter combination in three additions alternately with ricotta combination, starting and ending with flour combination, beating till simply mixed after every addition and stopping to scrape sides of bowl. Fold in pistachios and chocolate chips.
Spray a 10-cup fluted tube pan with baking spray with flour. Unfold batter into ready pan. Firmly faucet pan on a kitchen towel-lined counter to settle batter and launch any air bubbles.
Bake till golden brown and a picket choose inserted close to heart comes out clear, 1 hour to 1 hour and 10 minutes. Let cool in pan for 10 minutes. Invert cake onto a wire rack, and let cool utterly.
For topping: Within the bowl of a stand mixer fitted with the whisk attachment, beat all substances at medium-low velocity till thick and pipable, 2 to three minutes. Spoon topping right into a pastry bag fitted with a medium open star piping tip (Ateco #824), and pipe onto cake as desired. Garnish with pistachios and chocolate chips, if desired. Refrigerate in an hermetic container for as much as 3 days.
