Preheat the oven to 400 degrees F. Line a large baking sheet or 9x13 inch baking dish with parchment paper.
Prepare the tomato sauce: Place the cherry tomatoes and yellow onion on the baking sheet. Drizzle with 2 tablespoons of the olive oil, the balsamic vinegar, and season with the dried oregano, kosher salt, and freshly ground black pepper to taste. Toss well to coat, then spread out in a single layer. Do not put into the oven yet.
Prepare the garlic: Using a sharp knife, cut roughly ¼-inch off from the stem end of the head of garlic so that the individual cloves of garlic are exposed. Place the garlic in a square piece of foil, drizzle with the remaining 1 tablespoon of olive oil, then loosely wrap in the foil and place on the sheet pan with the tomatoes and onions.
Bake: Roast the veggies until they are tender, juicy, and the tomatoes are slightly golden in places, 30 to 35 minutes.
Blend: Cool the tomato mixture for 10 to 15 minutes, then remove the head of garlic from the foil packet and discard the foil. Once the garlic is cool enough to handle, use your fingers to squeeze the roasted garlic from the skin directly into a high-powered blender. Add the roasted cherry tomatoes and onions, along with their juices, to the blender and blend on medium-low until a smooth sauce forms, 1 to 2 minutes.
Feel free to add in more salt, or get adventurous and add a large handful of fresh basil leaves or heavy cream for a creamy pasta sauce! I also love to add in ½ cup of low-fat cottage cheese for a higher protein tomato sauce for my kids. Once you add your add-ins, blend again for 30 seconds, then serve as you’d like.
To store: Sauce is freezer-friendly and will keep well in an airtight glass container for up to 3 months.
