Place the egg yolks in a bowl and beat slightly. Set aside.

In a saucepan, add in the sugar, salt and cornstarch. Whisk to combine.

Add in the blood orange juice and whisk to combine. Turn on to medium heat and let it come up to a boil while whisking constantly.

Once it starts boiling, continue whisking and let boil for two minutes.

Pour half of the boiling mixture into the bowl with the egg yolks, whisking as you pour. That will help prevent the egg yolks from cooking.

Add the egg yolks and mixture into the saucepan and place back over the heat.

Let the mixture come back up to a boil and whisk and let boil for 5 minutes until thickened.

Remove from the heat and add in the zest and cold butter. Stir until incorporated.

Place the curd into a strainer with a shallow dish below it to catch the strained curd. Strain the curd for any cooked bits of egg.

Place plastic wrap on top of the hot curd and put in the fridge until completely chilled.