Prepare the base: Melt the butter in a saucepan and stir in 150 g of flour, mixing constantly.
Make the mixture: Add the hot milk gradually, whisking to avoid lumps.
Add the cheeses: Stir in the Grana Padano and Emmenthal. Season with salt, pepper, and grated nutmeg.
Chill: Mix well until homogeneous, then pour onto a plate. Chill in the refrigerator until firm.
Shape and coat: Once cooled, form the mixture into small balls. Bread each one successively in flour, egg white, and breadcrumbs.
Fry: Deep-fry in hot oil at 180°C until golden brown. Drain on paper towel.
Serve: Arrange the croquettes on a mesclun salad dressed with a light vinaigrette.