Spray a 7 inch springform pan with non-stick spray or lightly grease with butter.
Make the cheesecake filling by combining the room temperature cream cheese, sugar, sour cream, vanilla and salt in a blender. You can mix these ingredients in a regular mixer if you prefer. But, I have found that the blender creates a smoother cheesecake consistency. Make sure that you stop the blender and scraped the sides a few times so that all of the ingredients combine well. Once all ingredients are combined well, add in the egg and mix for another 5 seconds. The egg should be combined with the other ingredients, but you don’t want to over mix and add additional air. If you over mix and add too much air once the egg has been added, your cheesecake will be a much fluffier consistency and may overflow the pan when baking.
Make the carrot cake filing by combining all carrot cake ingredients except the carrots and walnuts in a mixer. Once all ingredients are well combined, add in shredded carrots and chopped walnuts and mix until all ingredients are combined.
Assemble the carrot cake cheesecake by pouring ½ of the carrot cake mixture into the greased springform pan-make sure that you swirl the pan around to get the carrot cake mixture to cover the entire bottom of the pan. Next, pour in half of the cheesecake mixture. Then, pour in the 2nd half of the carrot cake mixture and top off with the 2nd half of the cheesecake mixture. Lightly tap the filled springform pan on your counter to get rid of any air bubbles that there might be. 3-4 taps usually does the job. Wrap entire springform pan in foil. This will protect the top from any condensation that may occur and the bottom from any water that might seep in the bottom.
Cook the carrot cake cheesecake by pouring 1 cup of water into the Ninja Foodi. Place the trivet into the Ninja Foodi. Using a silicone sling or a homemade foil sling, place the carrot cake cheesecake on the trivet. Close lid and move valve to seal. Pressure cook on high pressure for 45 minutes. Once timer beeps, allow pressure to naturally release for 15 minutes and then quick release remaining pressure. Open lid and remove springform from Ninja Foodi.
Gently tap cheesecake on counter 2 or 3 times to remove any air bubbles that may have been created during the cooking process. Keep cheesecake on counter to cool for about an hour and then refrigerate for at lease 2 hours. If possible, refrigerate overnight.
Make frosting by combining butter, cream cheese, vanilla and salt in a mixer. Once combined add powdered sugar and milk. Once fully combined, decorate fully chilled cheesecake by spreading a thin layer of frosting on the top of the cheesecake and then sprinkling chopped walnuts on the frosting. Then, decorate the top with additional frosting using a piping bag and decorating tip.