Cut bread into 1" cubes. Select bowl that will fit into the Instant Pot's stainless steel inner pot. I used a metal bowl with sloping sides that is about 4" high and 7-1/2" wide across the top. Place a piece of parchment paper into the bowl, pressing flat any folds. Add cubes to lined bowl.
Place the following items into blender: milk (or cream), eggs, yolks, maple syrup (or low carb sweetener), vanilla and sea salt. Blend for 10 to 15 seconds, then, with motor still running, add melted butter through the door in lid.
Add 2 cups water to Instant Pot's stainless steel inner pot. Place trivet into Instant Pot. Place bowl with bread on top. Pour custard into bowl, pressing on bread gently so as to wet all the cubes. Place a small square of parchment paper over the surface of the pudding, and fold in any corners from the bottom piece that may be sticking out.
Place lid on IP. Seal and close vent. Press Steam button and adjust the time to 15 minutes. When timer goes off, allow the pressure to release on its own for 20 minutes; then press Cancel button and open pot.
Allow bowl to cool slightly, then remove pudding by lifting up on the corners of parchment that line the bowl. Transfer to a plate and flip over, so the bottom is the top. Slice and serve, with optional toppings.