Prepare the Pistachios: Put the shelled pistachios into a food processor and pulse until they are finely ground. Be careful not to over-process them, or you'll end up with pistachio butter! We want a fine crumb, not a paste.

Make the Pistachio Cream: In a mixing bowl, combine the ground pistachios, powdered sugar, softened cream cheese, milk, and vanilla extract. Use an electric mixer to beat everything together until it's smooth and creamy. If the mixture seems too thick, add a little more milk, a teaspoon at a time, until you reach your desired consistency. It should be spreadable but not runny.

Slice the Croissants: Carefully slice each croissant horizontally, almost all the way through, but leaving a small "hinge" on one side. Think of it like opening a book.

Fill the Croissants: Gently open each croissant and generously spread the pistachio cream inside. Don't be shy – use a good amount!

Optional: Warm them Up: Place the filled croissants on a baking sheet. If you want a slightly warm and even flakier croissant, you can bake them in a preheated oven at 350°F (175°C) for about 5-7 minutes. Keep a close eye on them – you just want them warmed through, not browned.

Garnish and Serve: Once they're out of the oven (or if serving at room temperature), sprinkle the tops with a little extra chopped pistachios and a dusting of powdered sugar, if desired. This adds a nice finishing touch.