Add the orange peels (making sure not to get the bitter white pith) into a food processor. Process until small and crumbly bits are formed.
Scrape down the sides of the food processor.
Add the granulated sugar and process again until the sugar and orange peel are completely combined.
Scrape down the sides of the food processor again.
Add the orange and sugar mixture to a medium bowl along with a pinch of salt.
Using a spoon or spatula, work the softened butter into the orange and sugar mixture until blended.
Add the fresh orange juice and orange extract (optional). Stir well. The mixture will look curdled, but don't worry about that.
Add the sugar, orange and butter mixture into a heavy bottom saucepan over very low heat. Stir frequently.
Meanwhile, separate 4 egg yolks (reserving the whites for another use) and whisk to combine.
While the orange and butter mixture is cooking over low heat, add the beaten egg yolks (a little at a time) to the heating orange mixture, stirring constantly.
Continue to add the egg yolks gradually to the saucepan, stirring constantly, until all the egg yolks are incorporated.
Continue cooking and stirring the orange curd over LOW heat until the mixture thickens and can easily coat the back of a spoon or spatula and a trail can be left behind after running a finger down the length of the spoon.*Note - this will take approximately 20 minutes of cooking on low heat. DO NOT be tempted to increase the heat to medium or you will cook the egg yolks, the eggs will scramble, and you will ruin the curd. Once the curd has thickened, pour it into a sieve placed over a bowl, and use a spatula to press the curd into the bowl.Discard the bits that are left behind in the sieve. Allow the hot curd to sit at room temperature until almost completely cooled.Curd will thicken upon cooling. Once almost completely cooled, cover the bowl with cling wrap and chill in the refrigerator at least 4 hours.The curd will thicken even more during chilling.
Spoon the chilled orange curd over pancakes, cake, toast, scones...you name it.