Pistachio Filled Croissants are almond croissants' sophisticated cousin. Day old croissants get new life when filled with a simple pistachio cream.
Chop ½ cup of roasted pistachios and place in a small saucepan with ½ cup of granulated sugar and ½ cup of water. Bring to a boil and turn down to medium-low and allow to simmer for 10 minutes.
Add pistachios to a food processor and blend until they resembles coarse sand. Using a hand mixer, or by hand, cream together the butter and sugar until light and fluffy, about 2 to 3 minutes.