Step 1

Grease a 6 × 3-inch round baking pan with softened butter; set aside.

Step 2

In a large mixing bowl, combine the melted butter, flour, 3/4 cup of the brown sugar, milk, 1/4 cup of the cocoa, eggs, baking powder, and vanilla. Using a hand mixer, beat until smooth. Pour the batter into the pan and sprinkle with the remaining 1/2 cup brown sugar and 1/4 cup cocoa powder.

Step 3

Pour 1 1/2 cups water into the Instant Pot. Place a trivet in the pot. Place the pan on the trivet. Carefully pour the boiling water on top of the batter. Do not stir.

Step 4

Secure the lid on the pot. Close the pressure-release valve. Select MANUAL/PRESSURE COOK and set the pot at HIGH pressure for 20 minutes. At the end of the cooking time, allow the pot to sit undisturbed for 10 minutes, then quick-release any remaining pressure.

Step 5

Serve warm with ice cream or whipped cream, if desired.