Preheat the oven to 300 degrees F. Line a large baking sheet (with sides) with aluminum foil.
In a large bowl, combine 1/4 cup olive oil, basil leaves, rosemary, red onion, and garlic. Spread mixture on the bottom of your prepared baking sheet.
Spread out the tomatoes (in a single layer) over the herb mixture on the baking sheet. Drizzled with remaining 1/4 cup olive oil, sprinkle with sugar, and season to taste with salt and pepper. Do not be afraid to use plenty of salt, as the salt helps to draw out their juices.
Bake 2 1/4 to 2 1/2 hours, turning the tomatoes several times. The tomatoes are done when their color deepens to dark scarlet and they taste mellow and very rich. Do not let the tomatoes brown. Also do not allow the garlic to brown, as it will turn bitter.
Remove from oven an transfer the tomatoes and their oil to a glass bowl. Cover and let them mellow at room temperature up to 2 hours. The flavors will ripen in this time.
Refrigerate the tomatoes up to 4 days, or freeze up to 3 months. Serve the tomatoes at room temperature, or tossed with hot pasta.
Makes a large batch.
* Use a good-quality canned tomato such as San Marzano, Muir Glen, Hunt's, Contadina, or Red Pack. Also be sure not to get the tomatoes packed in puree - you want only tomato juice.
Oven-Roasted Canned Tomatoes Recipe: https://whatscookingamerica.net/vegetables/ovenroastedcannedtomatoes.htm