In a bowl, beat the eggs until they become light and fluffy.
Pour in the fresh orange juice and mix well.
Add the sugar, ground cinnamon, and ground nutmeg, blending everything together.
In a saucepan over medium to medium-low heat, scald the heavy cream, bringing it just below boiling while stirring to avoid burning.
Gradually add ½ cup of the hot cream to the egg mixture, whisking continuously to combine.
Once well mixed, stir the egg mixture back into the saucepan with the remaining hot cream.
Cook over low heat, stirring constantly until the mixture thickens enough to coat the back of a spoon, being careful not to let it boil to prevent curdling.
Remove the saucepan from heat and add the softened butter if using, then pour the mixture into a bowl.
Allow the custard to cool, stirring occasionally.
Chop about half of the orange segments and drain them in a colander.
Gently fold the chopped orange segments into the cooled custard.
Transfer the mixture into a serving dish, cover with plastic wrap, and refrigerate for at least 2 hours to chill.
When ready to serve, top the chilled fool with the remaining orange segments.
