Rinse and halve the tomatoes, and put them in a pot along with brown sugar, white wine vinegar, salt, paprika, and Worcestershire sauce. 

Bring the tomatoes to a boil, reduce the heat, and let them simmer gently for 10 minutes.

Let the tomatoes cool slightly. Blend them into a smooth puree; this is easiest with an immersion blender directly in the pot.

Pour the tomato ketchup into clean jars or bottles, and seal them well. The ketchup can keep in the fridge for 2-4 weeks.

Tip: The ketchup can be flavored exactly as you like - for example, with fresh herbs, dried spices, or chili. Experiment with small tasting bowls until you get a ketchup that suits your taste perfectly. Or divide the ketchup into smaller portions that you flavor in different ways and store in small jars.