Melt the butter in a medium saucepan over medium heat. Add the finely diced Serrano ham and sauté for 2 minutes to render some fat.

Stir in the flour and cook for 2-3 minutes, stirring constantly to cook out the raw flour taste without browning it deeply.

Gradually whisk in the warm milk, a small amount at a time, ensuring the mixture is smooth and thickens before adding more.

Reduce heat to low and simmer the sauce for about 10 minutes, stirring frequently, until it becomes very thick and pulls away from the sides of the pan.

Remove from heat and stir in the grated Manchego cheese, nutmeg, and black pepper. Taste carefully before adding salt, as the ham is naturally salty.

Transfer the mixture to a shallow dish, cover with plastic wrap directly touching the surface to prevent a skin from forming, and refrigerate for at least 2 hours until solid.

Once the dough is cold and firm, shape it into small cylinders or oval logs.

Dip each log into the beaten eggs, then roll in breadcrumbs until fully coated.

Heat about 2 inches of vegetable oil in a deep frying pan to 350°F (175°C).

Fry the croquetas in small batches for 2-3 minutes or until they are golden brown and crispy.

Remove with a slotted spoon and drain on paper towels before serving warm.