You need egg yolks, gelatin, a whisk and a little elbow grease. And you must caramelise your puff pastry first − this is of dire importance to add the requisite textural contrast to the centre.
Choux pastry freezes well once it's cooked, so make the buns in advance if you prefer. For this recipe you will need a food mixer with whisk attachment or an electric whisk, a piping bag fitted ...