1.Wash and soak the red beans at least 8 hours or overnight. Longer soaking time can shorten the cooking time. Discard beans that float to the surface.
2.In a pot or pressure cooker add water and soaked red beans, the water should be higher than the level of red beans.
3.Turn the pot on high heat and bring it to a boil. Turn down the heat to simmer for around 1 hour until the red beans soften. For the pressure cooker, cook on high pressure for 40 minutes.
4.For a smoother paste, scoop cooked beans into a sieve and press down to form paste. Otherwise, transfer beans to a food processor and blend to a smooth consistency.
5.Transfer the paste into a pan and add salt, sugar, and butter. Keep burner on low and cook stirring constantly until the water has evaporated and forms a thick paste.
6.Let the paste cool down to room temperature before using. This paste can be stored in the refrigerator for about 2 weeks.