Place the strawberries in a bowl. Mix with 2 tablespoons of the orange liqueur and set aside.
In the top half of a double boiler, whisk the egg yolks and sugar to a creamy consistency. Place the egg mixture over hot water in the bottom of the double boiler, making sure that the pot containing the eggs doesn’t touch the water. Beat the mixture well with a whisk until it starts to thicken, about 5 minutes. Be careful not to beat too long, or you will cook the eggs. Remove from the heat and stir in ¼ cup of the liqueur, whisking until it’s well incorporated. Return to the double boiler and whisk until the mixture is thickened, 3 to 5 minutes. Remove from the heat and set aside.
Divide the strawberries among 4 wineglasses or dessert bowls, and spoon 1 tablespoon of the remaining orange liqueur over each. Top with the custard and decorate with a mint sprig, if you wish.
This dessert can be eaten warm immediately, or it can be refrigerated and eaten later, chilled.