In a large mixing bowl with an electric mixer fitted with a whisk attachment, beat ½ cup cold cream until stiff peaks form. Transfer to a medium bowl. Cover with plastic wrap and keep in the fridge.
In a large heatproof bowl, whisk together egg yolks, orange juice, salt, and ¼ cup sugar. Set the bowl over a pot of simmering water. Make sure the water is not touching the bowl. Whisk constantly until the sugar has dissolved, the mixture is lighter in color and doubled in volume, about 5 minutes (160˚F on instant thermometer). Remove the bowl from heat. Whisk in the chocolate until melted and smooth. Let it cool to room temperature, whisking occasionally.
In a large mixing bowl with an electric mixer fitted with a whisk attachment, beat the egg whites until foamy with uniform small bubbles. Add 2 tablespoons sugar and beat on high speed until stiff peaks form.
Fold the egg whites into the chocolate mixture in 2 additions. Fold in the whipped cream until just blended. With a piping bag, pipe the chocolate mousse into the 4 (5-ounce) containers. Cover each container with plastic wrap and chill in the fridge until firm, about 2 hours. Let stand at room temperature for 10 minutes before serving.
For the chocolate curls (optional), take a about 2-inch piece of chocolate and microwave in 50% for 15 – 20 seconds. With a vegetable peeler, scrape the blade lengthwise across the softened chocolate to create curls. Refrigerate until ready to use.
For the whipped cream, in a large mixing bowl with an electric mixer fitted with a whisk attachment, beat ¼ cup cold whipping cream until soft peaks form.
For the orange segments (optional), remove the orange peel and cut the white pith. Cut in between the membranes to release the segments with a thin sharp knife. Place the segments on a paper towel to absorb the juice.
To assemble, scoop a heaping tablespoon whipped cream over the mousse. Place an orange segment on top of the cream. Top with curls and orange zest, serve.