Line your muffin tin with paper liners and preheat your oven. For pressure cooker, place a trivet and a rack that fits your muffin pan inside.
In a large bowl, mix canned pumpkin puree, melted butter, sugar, vanilla, and egg. Whisk until smooth.
In another bowl, combine all-purpose flour, baking powder, baking soda, salt, and ground cinnamon. Mix well.
Slowly add dry ingredients into wet mix, stirring gently with a spatula.
For the swirl, mix extra melted butter, brown sugar, and cinnamon. Spoon batter into muffin cups, add swirl mix, and top with more batter.
Put muffin pan on trivet inside pressure cooker, add 1 cup water at bottom. Close lid, seal, and cook on high pressure for 15 minutes. Then natural release for 5 minutes and quick release.
Open lid carefully, test muffins with toothpick for doneness.
Notes
Ensure all ingredients are measured accurately. Serve muffins warm with coffee or tea.