In a large skillet, heat 2 tablespoons of extra-virgin olive oil over medium heat. Add the chopped onions and sauté until translucent, about 5 minutes. Add the chopped garlic and sauté for another minute until fragrant.
Stir in the chopped roasted red bell peppers and kosher salt. Cook for an additional 3-4 minutes, allowing the flavors to meld together.
Transfer the mixture to a blender or food processor. Add the remaining 2 1/2 tablespoons of extra-virgin olive oil, heavy cream, fresh basil, and balsamic vinegar. Blend until smooth. If too thick, add vegetable stock until desired consistency is reached.
Taste the coulis and adjust seasoning as needed, adding more salt or balsamic vinegar for extra zing.
Serve the Red Pepper Coulis warm or at room temperature. Store in an airtight container in the refrigerator if not using immediately.
