Soak beans overnight. Discard the soaking water and rinse three or four times under running water.
Place beans in pressure cooker with 2 cups of vegetable broth and cook 20 minutes from the time the pot whistles. Remove from heat.
Making the sauce: In a medium saucepan, ½ cup vegetable broth, garlic, pepper, and onion, and sauté for 10 minutes. Add the rest of the ingredients and let simmer until sauce thickens. Dice plantain and add to sauce.
Carefully open the pot making sure steam comes out completely first. Add the sauce to beans and mix well. Simmer in pressure cooker covered for about 10 more minutes in low-medium heat, and serve.