Step 1

In a medium saucepan set over medium heat, combine the sugar with the cornstarch and add in the juice.

Step 2

Cook, stirring, until thickened and bubbly. Gradually whisk in half of the hot mixture into the egg yolks to temper the eggs.

Step 3

Return the egg mixture to the saucepan and cook, stirring constantly, until the mixture thickens, about 2-3 minutes.

Step 4

Remove from heat and add in the butter pieces. Whisk until melted. Stir in food coloring if using.

Step 5

Pour the mixture into a small bowl and cover with plastic wrap pressed against the top. Chill for at least 4 hours, preferably overnight until set.