Add butter to the pressure cooking pot, select Sauté. When butter is melted add the oats and toast, stirring constantly, until they start to darken and smell nutty, about 3 minutes.
Add water, apples, brown sugar, cinnamon, and salt. Select High Pressure and set 10 minutes cook time.
When the cook time ends, allow the pressure to release naturally for 10 minutes, then finish with a quick pressure release.
When the valve drops, carefully remove the lid. Stir oats. Cover and let sit 5 or 10 minutes until oats are desired thickness.
Top with milk, nuts, and additional brown sugar, if desired.
