Melt butter and sugar in a heavy bottomed (or enamel) saucepan on low heat. Add lemon juice, salt and passion fruit pulp. Mix well.
In a bowl, whisk all 5 eggs lightly.
Increase heat to medium-low and add the eggs to the passionfruit mixture, whisking with a whisk. Continue cooking for a couple of minutes, whisking continuously. Once smooth, stir with a wooden spoon while cooking. The butter is ready when the mixture becomes thick and coats the back of the spoon (pouring cream consistency/store bought pouring custard consistency). Remove from heat.
Fill in lidded jars and store in the fridge for upto two weeks.
Notes
Because egg sizes may differ, if you find the mixture is too runny (slides off your spoon very easily), whisk in another egg and also add a tablespoon of butter. This helps thicken the butter to lemon curd consistency.