Swedish Sausage Stroganoff (a simple weekday meal)

Name: Swedish Sausage Stroganoff (a simple weekday meal)
Cuisine: European
Ingredients: 1 tbsp olive oil; 1 tbsp butter; 1 onion (finely chopped); 2 cloves garlic (finely chopped); 300g (10 oz) sausage; 2 fresh tomatoes (roughly chopped); 1 tbsp ketchup (or sugar); 1 tsp Worcestershire sauce; 2 tsp sea salt; ½ tsp oregano; ½ tsp paprika; ¼ tsp chilli powder; black pepper (to taste); 400g (14oz) tinned (canned) tomatoes; 100ml (3½ fluid oz) water or stock; 100ml (3½ fluid oz) cream; spinach (for serving - optional)