In a medium bowl, mix graham cracker crumbs with melted butter until fully combined. Pack firmly into the bottom of an 8" or 9" springform pan. Refrigerate for 30 minutes or bake at 350°F for 5 minutes.

In a large mixing bowl, use an electric mixer to beat the room temperature cream cheese until creamy and smooth, about 2–3 minutes. Gradually add the instant pistachio pudding mix, powdered sugar, and almond extract, mixing until thoroughly blended.

In another chilled bowl, beat the heavy cream on high speed until stiff peaks form, about 3–4 minutes.

Gently fold the whipped cream into the cream cheese mixture using a spatula. Start with a third of the whipped cream to lighten the mixture, then add the rest.

Spoon the filling onto the chilled graham cracker crust, spreading it evenly with a spatula. Cover and refrigerate for at least 6 hours, or overnight if possible.

Once set, remove the cheesecake from the refrigerator and the springform pan. Top with whipped cream and sprinkle with chopped pistachios before serving.