Heat the stock and infuse with the thyme for 5 minutes.
Add the melting salt and dissolve it in the stock.
Mix the cheeses with each other and add, stirring little by little, over medium heat.
Stir into a homogeneous mass with a whisk and pour directly into silicone moulds or pan sheet.
Cool back and cut into the desired shape.
Cover with flour, dip into egg whites and cover with breadcrumbs.
Deep fry the croquettes at 180°C in neutral vegetable oil or fat and serve immediately.