Rhubarb Barbecue Sauce - edible Southeastern Massachusetts

Ingredients

• 1 tablespoon extra-virgin olive oil
• 1 small onion (diced)
• Kosher salt (to taste)
• Freshly ground black pepper (to taste)
• 2 cloves garlic (finely minced)
• 1 tablespoon tomato paste
• ½ 14.5- ounce can low-sodium diced tomatoes (and their juices)
• ¼ cup light brown sugar (or to taste)
• 1 to 2 tablespoons apple cider vinegar
• 1 tablespoon Dijon mustard
• ½ to 2 teaspoons chipotle in adobo sauce (optional (see head note))
• 1 cup washed (dried, trimmed, and diced rhubarb (from about 3 or 4 stalks))