Preheat the oven to 425 F (218 C). Spread the peppers out on a baking sheet lined with foil (or a bare baking sheet brushed with oil) and roast for 15-20 minutes, flipping the peppers halfway to ensure even charring.
In a medium saucepan over medium heat, warm 2 tablespoons (30 ml // adjust if altering number of servings) of olive oil. Once hot, add the garlic and shallot, sautéing until softened and translucent — about 3 minutes. Lower heat to medium-low and add the cannellini beans and the salt and pepper. Mix well to combine and heat for 3-5 minutes or until the beans are warmed through.
Remove peppers from the oven and carefully wrap the foil around them to steam for a few minutes. Then carefully peel away the skin and remove the seeds, making sure to wash your hands thoroughly after.
To a food processor, add the bean mixture, charred peppers (start with just 1 if you prefer less heat), cashew butter, and lemon juice. Blend for about 1 minute, scraping down the sides as needed. Then, with the processor running, carefully stream in the remaining 3 tablespoons (45 ml // adjust if altering batch size) of olive oil until the mixture is creamy and smooth.