Bake the puff pastry at 425 degrees Fahrenheit for 12-15 minutes or until golden brown. Remove from the oven and let cool on a wire rack.
Once cool, use a paring knife to cut the puff pastry in half.
Using the prepared pastry bag and frosting tip, pipe the pastry cream into an even layer on half of the puff pastry.
Place the other half of the pastry on top so you've got yourself a nice little sandwich. Pipe a little flourish on top and finish with some chopped pistachios.
Serve immediately. Pastries can be stored up to a day in the fridge. If making this recipe in advance, wait to cut in half and pipe until ready to serve.