Zest orange, then cut them in half and squeeze to juice them.
Combine orange zest, juice, and sugar in a medium saucepan.
Add salt, extract, and cornstarch, cook over medium heat, stirring constantly.
After 5 minutes the sugar should be dissolved and the mixture should come to a gentle boil.
Whip the egg yolks in separate bowl and temper them with half the hot orange juice mixture.
Pour the egg and juice mix back into the saucepan. Turn heat to low. Continue stirring about 8 to 10 minutes – the foam from whipping the egg mixture will disappear and it will start to thicken.
Continue to stir until it coats the back of your spoon or spatula.
Remove from heat and stir in butter.
For a smoother texture pour and smoosh through sieve.
Cool to room temperature before using.
Store in an airtight container in the refrigerator.
Notes
Can add orange color if you want a more vibrant color.