Ham & cheese croquetas

Name: Ham & cheese croquetas
Prep time: 20 min
Cook time: 1 h 25 min
Total time: 1 h 45 min
Cuisine: Spanish
Ingredients: 25g butter; ½ small onion finely chopped; 50g plain flour; 250ml milk; 140g sliced smoked ham diced; 50g mature cheddar coarsely grated; 50g gruyère finely grated; 1 tsp Dijon mustard; 2 tbsp double cream; 2 large eggs; 140g fine dried breadcrumbs; sunflower oil for deep frying; 300g ripe tomatoes roughly chopped; 1 long red chilli finely chopped (deseeded if you don't like it too hot); 1 small red onion finely chopped; 4 large garlic cloves crushed; 100g demerara sugar; 100ml red wine vinegar