• Preheat oven to 350 Deg F. You can wait to do this step if you chill the dough first. Prepare baking pans with parchment paper. 
• Cream butter and sugar together in either a large mixing bowl with a hand mixer or using a stand mixer. Add in the passionfruit juice and vanilla extract and mix again until well combined. Sift together the flour, corn starch and salt then add this to the butter mixture and mix until fully incorporated. The dough will be soft and just barely sticky. You can either shape the cookies at this point or chill for half an hour or so. They won’t spread out if not chilled, but I find chilling just a little bit helps them be less sticky when rolling and pressing. 
• Make the buttercream next
• In either a large mixing bowl or using a stand mixer, cream together the butter and powdered sugar. Add in the vanilla bean paste and salt if using unsalted butter and mix well until very smooth. Add in heavy cream or milk a tablespoon at a time until you reach the consistency you like. It should be stiff but not too stiff you can’t pipe it onto the cookies. Prepare a piping bag with a #12 sized piping tip - either round or open star, and fill with the buttercream. Tie the top with a rubber band or piping bag clip and set aside until ready to use. 

To make the cookies:

• Roll out spoonfuls about 16 grams each - about two teaspoonful, and roll into a ball. Place a few inches apart on a cookie sheet lined with parchment paper. Using a fork, dip the underside in a little flour then lightly indent into the cooking, pressing it about halfway down the dough, repeat with the rest of the cookie dough balls. 
• Bake the cookies for 10-12 minutes, you don’t want to overtake them and make them too golden brown or else they will be too firm. These will be a pale colored cookie once baked.
• Once baked, let cool for a few minutes on the baking sheet then transfer to a wire cooling rack to cool completely. 
• When ready to assemble, pipe a circle of buttercream around the bottom of one cookie, spoon about a teaspoon of the curd into the middle then gently place the other cookie on top to make a cookie sandwich. 
• Set the cookie sandwiches on a tray and freeze until set. Transfer to an airtight container and keep chilled, either refrigerated or frozen. Thaw slightly before eating.