Generously coat a 3-cup fluted tube pan with baking spray.
In a small saucepan melt the chocolate over low heat. Set aside to cool.
In a small bowl stir together the flour, baking powder, and salt; set aside.
In a medium bowl beat the butter on medium speed for 30 seconds. Add the sugar and beat on medium for 1 to 2 minutes or until well combined.
Add the eggs, one at a time, beating well after each addition. Beat in the vanilla.
Add flour mixture and beat just until combined. Transfer half of the batter (about 1 cup) to a small bowl; stir in the melted chocolate.
Stir peanut butter into the remaining batter. Alternately drop spoonfuls of chocolate and peanut butter batters into the prepared pan.
Using a table knife, gently cut through batters to swirl them together (do not overmix).
Place the trivet in the Instant Pot. Add 1 cup of water to pot. Place the cake pan on the trivet. Secure the lid on the pot.
Close the pressure-release valve. Select Manual and cook at high pressure for 25 minutes. When cooking is complete, use a quick release to depressurize.
Carefully remove the cake from the pot. Let the cake cool on a wire rack for 10 minutes, then remove cake from pan and let cool completely on a wire rack.
Drizzle with Ganache or Peanut Butter Glaze. If using Peanut Butter Glaze, sprinkle with peanuts if desired.
In a small saucepan bring whipping cream just to boiling over medium heat.
Remove from heat and add the chocolate. Do not stir.
Let stand for 5 minutes. Stir until smooth. Cool for 15 minutes before using.
In a small bowl stir together the powdered sugar, peanut butter, and enough milk to make a thick drizzling consistency.