In a medium saucepan, whisk eggs, egg yolks and sugar together until smooth. Whisk the corn starch together with a bit of the blood orange juice to create a slurry.
Whisk the blood orange juice, the lemon juice and the slurry into the egg mixture.
Continue to whisk over medium heat until thick, 10-15 minutes. It should be the consistency of pudding. Make sure the whisk hits the bottom of the pot to keep the bottom from burning. This is less likely to happen if you use a heavy bottom saucepan.
Over low heat, slowly whisk in pieces of the butter.
Move the curd to a bowl and allow to chill in the refrigerator. It will continue to thicken as it cools.
Once cool, whisk in the additional 1/4 cup of blood orange juice if desired for flavor or to thin out the curd.
Store extra curd in the refrigerator with plastic wrap pushed directly against the curd to prevent a skin from forming.