Add the cashews to a bowl and cover with boiling water. Set aside while you prep the remaining ingredients. If you have had trouble with cashew based sauces in the past, you can boil them in a pot for about 20 minutes while you prep all other ingredients which helps to soften them further.
Preheat the oven to 350 degrees Fahrenheit.
Peel the garlic, and chop the onion and bell peppers into large chunks.
Place on a silicone baking mat or parchment paper and roast for 30 minutes.
While the veggies are roasting, cook your pasta of choice.
When the veggies are done, add to a high speed blender with the drained cashews and all remaining ingredients and process until completely smooth. Start with 3/4 cup of milk and add more as needed to thin it out.
Stir the sauce into the cooked pasta, and top with fresh basil if desired!