In a small saucepan over medium heat, reduce the orange juice by boiling for about 10-12 minutes until halved. Set aside to cool.

In a separate saucepan over medium-low heat, whisk together sugar, cornstarch, and baking soda. Gradually add milk, whisking to prevent lumps. Heat until steaming, about 5 minutes.

Whisk egg yolks in a small bowl. Slowly add about ¼ cup of warm milk mixture to temper the eggs, whisking constantly.

Pour the egg mixture back into the saucepan with remaining milk, stirring constantly. Cook over medium-low heat until thickened, about 5-7 minutes.

Remove from heat. Whisk in cooled orange juice, vanilla, orange zest, and butter until smooth.

Pour custard into 3 small cups or ramekins. Cool to room temperature for 30 minutes, then refrigerate at least 3 hours or overnight.

Top with whipped cream when ready to serve. Garnish with fresh mint and extra orange zest.