Start by getting the passion fruit juice ready. Cut fruit in half and scoop out juice and seeds into a large strainer over a bowl. Using a spatula or the back of a spoon, press the juice through the seeds. Continue pressing and stirring in the strainer until the seeds are as dry as you can get them and you've obtained all the juice you can get into the bowl. Dump seeds and set juice aside.

Place egg yolks, passion fruit juice, sugar and lemon juice into a small sauce pan and gently heat until the sugar is melted, whisking constantly. Do not heat too high as you don't want to curdle the eggs nor have the sauce 'break.' (This means it will start to separate and look oily and 'broken.')

Once sugar is dissolved, add in stick of butter (in small chunks) and whisk until butter is completely melted. Gently bring to simmer until sauce is thickened, approximately 7-9 minutes.

Pour into a bowl, place a layer of plastic wrap on top and refrigerate until chilled.