Dice the red onion and add to a small pot over medium-low heat. Gently saute 3-4 min until beginning to turn translucent.
Add minced garlic, oregano, salt, and tomato paste. Continue to saute 4-5 min until the raw garlic smell is gone and the onion is completely cooked through. Lower the heat if the onion begins to brown.
While the onion is cooking, WEAR GLOVES and prepare your habaneros. I do not recommend handling with bare hands. Set aside, this is blended into the sauce raw.
Once the onion has cooked down, add the annatto and sour orange juice. Bring to a simmer and cook for 5 more minutes. Taste for salt and add more if you prefer.
Add the cooked ingredients to your preferred vessel for stick blending and add the butter and prepared habaneros. I prefer to stick blend this recipe as it makes a little under 2 cups. If you use a normal sized blender, treat appropriately as this is a hot liquid. Prop the lid part way and cover the vent with a paper towel or kitchen towel. Blend on a low setting first, then high to puree. Serve or refrigerate.