Preheat the oven to 375 F. Slice the tomatoes making sure to remove the stems. I usually just slice them in half. Peel the garlic. Divide the tomatoes and garlic cloves evenly between 2 sheet trays, Drizzle over a good amount of olive oil over each tray. About 1/4 cup for each. Then salt and pepper generously. I like a generous pinch of diamond kosher salt for each tray and fresh crackled pepper. Then roast for 60 minutes.
While the tomatoes are roasting, prepare the croutons. Cube the bread, then coat with remaining 1/4 cup of olive oil. The bread will really absorb the oil so be generous so the croutons really toast. Top with salt, pepper, oregano and garlic powder and toss to coat.
When the tomatoes are done roasting, remove them from the oven to cool. Place the croutons on the middle rack and toast for 20 minutes. Flip half way. If they are not browned then leave in for longer, but be careful not to burn them.
Once the roasted tomatoes and garlic are cooled enough for you to handle the sheet trays with your bare hands, scoop the tomatoes and garlic into a blender. I like to do this in 2 batches. Blend on high until it is a smooth consistency. Add a few tbsp of water if the mixture is too thick to blend.
Place a fine mesh sieve over a large bowl or storage container and sieve the tomato puree to remove any seeds or texture. You want it to look like a can of tomato concentrate. I find it helpful to do this a little bit at a time and stir the mixture so it will go through the sieve. You may need to rinse the sieve between batches. At the end you should have around 2 L of tomato puree concentrate.
For making the soup, use a 3:1 ratio of tomato puree to whole milk. so I put 3 cups of puree in a medium sauce pan then added 1 cup of whole milk and heated until simmering. Taste for salt and pepper before serving. Top with the homemade croutons and enjoy!
