Is it possible to make french fries out of potatoes and tomatoes?
I can think of two approaches. In either case, you are going to want to use dehydrated tomato powder (or ketchup powder), as you certainly don't want to add the water content of the tomato to your fry. Option one would be to mix the tomato powder into a mashed potato, structure that with some hydrocolloid, and fry. The other, much simpler and probably better approach would be to season with a powdered-tomato spice mix immediately after frying.