Add the butter to the Instant Pot and press “Sauté.” Once the fat has melted, add the mushrooms, onion, garlic and thyme, sautéing for 10 minutes until lightly caramelized. Add the kale and sauté for another 2 minutes just until wilted. Press the “Keep Warm/Cancel” button.
With butter, grease a 1½-quart (1.5-L) casserole dish (I use one with a glass lid- see below in Recipe notes) that fits inside the Instant Pot. Set aside.
In a large mixing bowl, whisk the eggs and cream together until the eggs are fully incorporated. Add the sea salt, raisins, lemon zest, ¾ of the cheese (reserving the rest for the top) and the mushroom-kale mixture, gently stirring to fully combine. Pour the mixture into a greased casserole dish. Evenly drop little dollops of ricotta into the custard filling.
Place the glass lid on top of the casserole dish. Place the Instant Pot trivet inside the Instant Pot. Pour 1 cup (237 ml) of water into the Instant Pot. Carefully transfer the covered casserole dish to the Instant Pot on top of the trivet. Place the lid on the Instant Pot, making sure the steam release valve is sealed. Press the “Manual” setting and decrease the time using the “-” button until you reach 20 minutes.
When the Instant Pot is done and beeps, press “Keep Warm/Cancel.” Allow the Instant Pot to release pressure naturally for 10 minutes. Using an oven mitt, “quick release”/open the steam release valve. When the steam venting stops and the silver dial drops, carefully open the lid.
Carefully remove the casserole dish from the Instant Pot and remove the lid. Next, add the leftover cheese to the top of the quiche. Either place the Instant Pot lid back on the Instant Pot for about 3 minutes to melt the cheese or carefully remove the casserole dish and place under a preheated broiler for 3 to 5 minutes to brown the cheese on the top.
Serve hot or warm.