Begin by adding 1 cup of water to the bottom of your Instant Pot. Place the trivet inside to create a steaming surface. Close the lid and set the pot to the 'Saute' function briefly, just to warm it up.

Take a 7-inch round cake pan and thoroughly grease it with butter or cooking spray. Wrap the pan tightly with aluminum foil.

In a large mixing bowl, beat together the softened butter and sugar until light and fluffy. Add in the large egg and reduced fat sour cream, mixing until smooth.

Gradually add half of the cornbread mix into the wet mixture, followed by the milk. Stir gently until just combined, then fold in the remaining cornbread mix.

Gently fold in both the whole kernel corn and creamed corn until just incorporated.

Pour the batter into your prepared pan, smoothing it out evenly across the top. Cover the pan loosely with aluminum foil.

Carefully place the pan on the trivet inside the Instant Pot. Set the timer to cook on high pressure for 50 minutes.

Once the cooking time is complete, carefully perform a quick release of the pressure by turning the valve. Let your casserole stand for an additional 15 minutes.