I usually use 6 – 8 whole medium sized Globe/Slicing Tomatoes for sauce. That's about two 14.5 oz cans worth. For Romas, it's more....about 12-14. Some people peel the tomatoes first, which can be a pain. To do so, blanch them whole in hot water for 1-2 minutes, remove to cool a bit, then begin peeling the skin off.
Or just roast them whole and peel the skin once they are done (they have collapsed a bit but still hold their shape).
Personally, I don't peel mine. I cut my tomatoes in half and roast them cut side up at 350 – 400 for 30-45 minutes. Once they start to collapse a bit, I know they’re done. Take them out to a plate to cool, and save any pan juices that have collected. Once the tomatoes are cool, put them in a blender or food processor with the collected juices and puree. Sometimes I add a splash of wine and a few cloves of garlic to the processor as well.
With 6 – 8 tomatoes, I use around 2 cups of liquid (more or less depending on consistency desired). Usually 3/4 cup chicken stock and the rest (1 1/4) wine. A red is good, but I often use a sweet white since I have it on hand most often, and typically don’t have to add extra sugar when using a sweeter wine.
When using a food processor to puree the roasted tomatoes, you don’t have to use a slow cooker to break the tomatoes down since they already are. You can instead go straight to the pot and begin making your sauce. Or, use the slow cooker if you want to just start the sauce and walk away. I’ve done both depending on my mood and schedule.
If your sauce isn’t as thick as you like, you can thicken it with tomato paste (from a can) or a slurry of corn starch and cold water. On occasion I’ve use a slurry of cornstarch, and I typically add a little (about 1/8 a teaspoon or less…..small shake or pinch if you will) of tomato bullion powder to the slurry. I’ve got a 7.9 oz jar of it made by Knorr. It’s great for stuff like this, but it is a bit salty, so go easy with it if you find it and use it.
Speaking of tomato bullion - Another great use for it is to add some to your rice water as the rice cooks. It gives the rice a great flavor and turns it a pinkish color. This is wonderful for beef stew and rice or chili and rice. I sometimes also add it to my pasta water. You can even sprinkle some into your ground beef if you’re making meatballs, taco meat, meat sauce for spaghetti, etc.
A strange little treat for myself that some may find weird is to make some rice with the tomato bullion in the water. Sautee some diced onion and jalapeno (occasionally bell pepper as well) in oil as the rice cooks. Then mix the rice, peppers and onion together and slather with hot sauce for a moist rice dish and chow down. I love it. It’s a nice alternative to Spanish rice on taco night too. Good stuff.