Swedish meatballs

Name: Swedish meatballs
Cuisine: European
Ingredients: 1 brown onion, left whole, peeled; 2 slices soft white sandwich bread, crusts removed, cut into 1cm cubes; splash of milk; 300g beef mince; 300g pork mince; 1 egg; 0.25tsp freshly grated nutmeg; 0.25tsp allspice; 0.25tsp black pepper; 0.75tsp cooking salt; 1 tbsp vegetable oil; 50g unsalted butter; 3 tbsp plain flour; 2 cups low salt beef stock; 125ml double cream; Finely chopped chives; Tenderstem broccoli; Maris Piper potatoes; Whole milk; Unsalted butter