I've got the rest of the recipe, sugar, vinegar and a few other spices that I was going to experiment with,but I wanted to know what do you need to do to the tomato in order to get it to look like ketchup, not a tomato sauce? 
Roasting the whole tomatoes, seaoned and cut into halves, perhaps with some unpeeled garlic/rough chopped red onions/herbs (the first I would say is essential), then passing the results (after picking out the extras) through a seive or conical strainer, rubbing through the pulp with the back of a wooden spoon or spatula- creating a passata- can give a much deeper taste than fully preparing before cooking.   Plus it's way less fiddly. :) 