Prepare the springform pan for a water bath. Once the crust has cooled, wrap the springform pan with 2 layers of heavy-duty foil wrapping and folding the edges at least ¾ up the sides of the pan. For an extra barrier, if desired, place an oven bag around the foil and tie it around the foil to secure it.
Combine the softened cream cheese and sugar in the bowl of a stand mixer with a paddle attachment (or use a hand mixer) and mix on medium until smooth, about 2-3 minutes, scraping the sides of the bowl occasionally.
Add the pistachio butter and mix until combined. Add the eggs one at a time, mixing well after each. Then add the vanilla and salt and mix well.
Add the heavy cream and mix until combined, about 30 seconds.
Pour the batter into the prepared pan over the crust.
Place the springform pan into a roasting pan and place in the oven. Carefully pour very hot water into the roasting pan until it comes about halfway up the sides of the springform pan, being careful not to get any water between the pan and the foil.
Bake the cheesecake at 325 degrees F for 80 to 90 minutes. If you have an instant-read thermometer, the temperature should be 150-155 degrees Fahrenheit. The cheesecake is done when the middle is still slightly jiggly but the edges are fully set.
Turn the oven off and slightly prop open the oven door with a wooden spoon if it won’t stay open on its own. Allow to cool in the oven for 1 hour.
Carefully remove the roasting pan from the oven and remove the cheesecake from the water. Remove the foil. Cool for another 30 minutes on a wire rack.
Place the cheesecake in the refrigerator, covering the top with foil or plastic wrap and chill at least 4 hours or overnight. Top with the fresh whipped cream and sprinkle with pistachios before serving.