In a medium bowl, mix together the flour, baking powder, baking soda, and cornmeal. Set that aside.
Spray the springform pan with cooking spray or wipe the springform pan with butter.
In a liquid measuring cup, add the milk and vinegar. Let that sit for 5 minutes.
In a large bowl, add the sugar, cooled melted butter, and egg. Mix well until fully combined.
Add the milk and vinegar mixture and stir again.
Mix in the dry ingredients into the wet ingredients. Stir until just combined. Do not overmix as this will create a tough cornbread.
Pour the batter into the springform pan. Cover tightly with aluminum foil.
Add 1 cup of water to the bottom of the Instant Pot. Place the springform pan on the Instant Pot trivet insert and carefully lower it into the Instant Pot.
Close the lid of the Instant Pot and pressure cook on "high pressure" for 50 minutes. Naturally release the pressure for 10 minutes. Carefully remove the cornbread from the Instant Pot and allow it to cool on a wire rack. Serve hot or at room temperature.