STEP 1

In a small bowl, mix the cornstarch into ¾ cup of the milk until smooth and set aside. 

STEP 2

In a medium saucepan, warm the remaining milk and keep on low heat until needed. 

STEP 3

Heat a medium sized pot over medium-low heat, add the butter and olive oil, and sweat the onions until soft and translucent. Add jamón and lightly sauté for 1-2 minutes. 

STEP 4

Slowly add the flour to the pot, stirring constantly with a wooden spoon. Allow mixture to cook, stirring frequently, for about 5 minutes, until fragrant. Do not allow to brown. Add the milk in a steady stream, whisking constantly, then add the cornstarch mixture and season with the nutmeg. Mix well, reduce heat to low, and allow to cook, stirring constantly, for about 5 minutes, until the mixture is very thick. Stir in the grated cheese and mix until melted, about another minute or so. Pour onto a baking sheet with a 1-inch rim and spread out evenly.  Allow to cool at room temperature for one hour, uncovered.  

STEP 5

Transfer the cooled mixture to a piping bag fitted with a 1 inch round tip. Evenly cover a second sheet tray with about 1/2 -inch layer of flour.  Pipe the mixture onto the floured tray to form long sticks. You will have about 5-6 sticks when finished. Refrigerate until very firm, about 1-2 hours. 

STEP 6

Cut each stick into 2-3 inch logs and toss well in flour to coat all sides. In a shallow dish, beat the eggs with 2 tbsp cold water and place breadcrumbs in a wide, shallow dish.  Pat the excess flour from each croquette, roll in the egg mixture and then the breadcrumbs until well coated. Arrange on a clean tray and refrigerate until needed.  

STEP 7

Fill a large, shallow heavy pot or wok with 2-3 inches of oil. Heat oil to 350°F and fry the croquetas in batches, avoiding crowding, until golden brown on each side and hot and creamy within. Drain well on absorbent paper and serve warm with the alioli on the side.