In a large mixing bowl, whisk together the egg, oil, buttermilk, molasses, and sugar.
Stir in the flour, cornmeal, baking powder, allspice, walnuts, and raisins.
Pour the batter into the prepared pan and cover the pan with foil.
Place 1.5 cups of water in the Instant Pot. Place a steamer rack in the pot. Place the pan on the rack.
Close the lid and set the Instant Pot to cook on HIGH PRESSURE for 30 minutes. At the end of the cooking time, allow the pot to rest undisturbed for 10 minutes.
Open the lid and carefully remove the pan. Allow the pan to cook a little. Run a knife along the edge of the pan, and then unmold the bread. Slice and serve.
It's absolutely imperative that you grease the bundt pan before cooking the bread unless you're a fan of eating your bread in shredded form, as that's what it's going to take to get the bread out of the pan at that point.
When you take the bundt pan out of the Instant Pot, make sure to let it rest for at least 10 minutes before serving. The residual heat will further cook the bread and the bread is much easier to remove from the pan when it has had a little time to cool.
Try spreading a little cream cheese on the brown bread! The tang and creaminess of the cream cheese help balance out the rich sweetness of the molasses.