For the orange curd: In a medium saucepot, whisk the egg yolks and granulated sugar together until pale yellow and slightly thickened and the whisk leaves lines behind it. Next, whisk in the orange juice and zest. Set the pot over medium heat and cook, stirring constantly with a rubber spatula, just until the mixture is thick enough to coat the back of a spoon and holds its shape when you drag your finger through it, 8 to 10 minutes.
Remove the pot from the heat and stir in the butter until completely combined. Pour the curd into a bowl and let cool to room temperature. If any of the curd got slightly overcooked, put it through a fine-mesh strainer to remove any set egg yolk.
Cover the curd with plastic wrap pressed directly to the surface and refrigerate for at least 4 hours. (The curd will hold well for up to 4 days.)
For the meringue: Position a rack in the middle of the oven; preheat to 300 degrees F. Line a large rimmed baking sheet with a silicone baking mat.
Stir together the cornstarch and lemon juice in a small bowl until the cornstarch completely dissolves. Set aside.
Place the egg whites and salt in the bowl of a stand mixer fitted with the whisk attachment. Whip on medium-high speed until the egg whites are frothy. With the machine running, slowly stream in the granulated sugar. Increase the speed to high and whip the egg whites until you see ribbons left in the meringue by the whip attachment. Pour in the cornstarch mixture and whip a few seconds more, until stiff peaks form and the meringue becomes very glossy.
Mound the meringue in the middle of the baking mat and spread it into a 10-inch round using a small offset spatula -- the shape needn't be perfect, but make sure to spread the meringue in an even layer.
Bake for 10 minutes, then drop the oven temperature down to 200 degrees F. Bake for an additional 45 to 50 minutes. The meringue is done when the top is set and not tacky to the touch, and when a small offset spatula can be slid underneath and come out clean or with very little meringue attached. Turn off the oven, crack the door, and let the meringue sit for an additional 30 minutes.
Remove the meringue from the oven; run a large offset spatula around the circumference to release it from the baking mat. Set a serving platter beside the baking sheet and gently slide the meringue onto the platter. Let sit at room temperature until ready to assemble.
For the vanilla whipped cream: Combine the cream, confectioners' sugar and vanilla paste in the bowl of a stand mixer fitted with the whip attachment. Beat on high speed until soft peaks form. Refrigerate for up to 30 minutes before serving.
To assemble: Spoon the curd into the center of the meringue and spread it in an even layer, leaving a 1-inch border. Spread the whipped cream over the curd. Top decoratively with the clementine and grapefruit wheels. Garnish the entire pavlova with the lime zest and serve immediately.