Spray a 7 x 3-inch round cake pan generously with cooking spray. (See the link in the post for the pan we used.) Set aside.

In a medium bowl, whisk together the cornmeal, flour, baking powder, and salt. Set aside.

In a microwave safe container, melt the butter. Meanwhile, in a small bowl, whisk together the buttermilk, milk, and egg. 

Pour the milk mixture into the dry ingredients and stir to combine. They batter should resemble pancake batter. Add the melted butter and mix well until all the butter is incorporated. 

Pour the batter into the greased cake pan, and cover with aluminum foil. Place a trivet in the inner liner of the pressure cooker. Then add 2 cups of water. Using a foil sling, carefully lower the cake pan onto the trivet. 

Close the lid and turn the valve to sealing. Use the manual/pressure cook button and set the timer to 35 minutes on high pressure. After the time is up, allow the pressure to release naturally. (I've waited as long as 30 minutes before opening the valve.)

Open the lid, and use the sling to carefully remove the cake pan from the pressure cooker. Set the pan on a heat-safe surface, and allow to cool in the pan for 10-15 minutes. Use a knife to run along the edges of the pan to loosen the cornbread. Place a serving platter or plate over the pan, and flip it over. The cornbread should come right out.

Serve the cornbread immediately or store in an airtight container for up to 2 days.