Dice butter and melt in a pot. Wash the orange hot and rub dry. Tear off half of the orange peel in zests. Halve the orange and squeeze 1 half. Remove butter from the stove, pour through a fine sieve and let it cool down a little.
Beat the egg yolks, saffron, orange zest, 4-5 tbsp. orange juice and white wine over a hot water bath until frothy. Gradually add sugar, salt and curry to taste.