Line the bottom of a 7-inch cake pan with a removable bottom with parchment paper. Coat the sides of the pan and the parchment paper with cooking spray.
Add the pistachios and ½ tablespoon of butter to a food processor and pulse for 2 to 4 seconds until the pistachios are chopped finely with crumbly textures. Pour the pistachios into the prepared cake pan and spread it all around the bottom pressing it gently with the tip of your fingers to form even layer of crust. Place the cake pan in the freezer while you prepare the remaining ingredients.
Pour 1 cup water into the Instant Pot and place the wire-metal steam rack in the pot.
Make the cake batter
In a large bowl, first mix all the dry ingredients - sugar, flour, and cardamom.
Then stir in the ricotta and rose essence until well combined. Add the eggs, one at a time, and stir after each addition until just combined.
Pour the batter into the prepared pan. Add the food coloring and gently swirl through the batter with a toothpick.
Cover the pan and pressure cook
Cover the pan with a paper towel and place an 8-inch sheet of aluminum foil over the top, crimping down the foil around the sides of the pan to secure the paper towel in place.
Place the pan on the rack in the Instant Pot. Secure the lid and set the Pressure Release to Sealing. Select the Pressure Cook or Manual setting and set the cooking time for 40 minutes at high pressure.
Let the pressure release naturally; this will take 10 to 15 minutes.
Take the cake out and chill
Open the pot and, wearing heat-resistant mitts, lift out the cake pan. Remove the foil and paper towel, then dab off any liquid that may have accumulated on top of the cake with another paper towel. Let the cake cool on the counter for about 1 hour (the cake will continue to cook as it cools).
To remove the cake from the pan, carefully run a butter knife around the inside edge of the pan and down the sides. If your pan is a push pan type, place it on an empty glass cup and gently push down on the top edges of the pan. This will help the cake to release from the pan sides. If using a springform pan, unclasp the collar on the pan and lift it off.
Transfer the cake to a platter. Garnish with sliced pistachios (optional). Refrigerate for at least 4 hours and up to 5 days.
Cut into wedges and serve cold.
Ricotta Cheesecake stays well refrigerated for up to 10 days in an airtight container. You can also freeze it for longer shelf life.
You can freeze Ricotta Cheesecake up to a month by placing it in a freezer-proof container or wrapping it in a foil and then keeping it in a freezer zip lock bag. To defrost keep the cake overnight in the refrigerator to thaw.
For a nut-free recipe, skip the pistachio crust and garnish. Follow the same cook times and the cheesecake comes out equally delish.
To bake this cake, preheat the oven to 350 degrees F. Bake for 40 mins or until the sides are golden brown and the wooden skewer comes out clean. Also depending on the size of the cake pan, the cooking time will be more or less.