Heat the oven: Preheat to 350°F (175°C). Place a rack in the center.

Make the crust: Crush the graham crackers into fine crumbs. Stir in the sugar and melted butter until the texture looks like wet sand. Press the mixture firmly into a 9-inch pie dish, going up the sides.

Par-bake the crust: Bake the crust for 8–10 minutes, until lightly golden and fragrant. Let it cool for 10 minutes while you make the filling.

Prepare the citrus: Zest one sour orange to get 1 tablespoon zest. Juice enough oranges to get 3/4 cup juice. Strain the juice to remove seeds and pulp for a smooth custard.

Whisk the filling: In a medium bowl, whisk egg yolks until slightly thickened and pale, about 1 minute by hand. Add sweetened condensed milk and whisk until smooth. Stir in the sour orange juice, zest, vanilla, and a pinch of salt. The mixture will loosen, then thicken slightly as it sits.

Fill and bake: Pour the filling into the warm crust. Tap the pan gently on the counter to pop air bubbles. Bake for 12–15 minutes, until the edges are set and the center has a slight wobble.

Cool and chill: Let the pie cool on a rack to room temperature, about 1 hour. Cover and refrigerate for at least 3 hours, preferably overnight, until fully set.

Make the whipped cream: Whip the heavy cream with powdered sugar until soft peaks form. Keep it soft and silky, not stiff.

Serve: Slice the chilled pie with a warm, clean knife. Top each slice with a dollop of whipped cream. Garnish with extra zest or thin orange slices if you like.