Croquetas de Chorizo (Spanish Chorizo Croquettes)

To make the chorizo filling:

1. Place a large saucepan over medium heat. Add the diced chorizo (do not add butter or oil) and cook, stirring often, until heated through and golden.
2. Transfer the chorizo to a towel-lined plate to drain and place the saucepan back over medium heat.
3. Add the butter and olive oil to the heated pan. Once the butter has melted, add the diced onions and cook, stirring occasionally, until softened and translucent, but not browned.
4. Whisk in the flour to form a paste and cook, stirring the sides and bottom, until golden, about 3 minutes.
5. Slowly whisk in the milk, a little at a time to prevent lumps, until incorporated. Cook the mixture while stirring until thickened, about 10 minutes. Stir in a pinch of nutmeg and season with salt and pepper to taste.
6. Fold in the drained chorizo, simmer while stirring for about 5 more minutes to incorporate the flavor, then remove from heat.
7. Once the mixture has cooled, transfer to a bowl, cover, and refrigerate for at least 6 hours to overnight.

To assemble and fry:

1. In a shallow bowl, beat the eggs together.
2. Place the flour in another shallow bowl and the breadcrumbs in a third bowl.
3. Fill a pot with oil at least 1 inch (2.5 centimeters) deep and place over medium heat.
4. Line a baking sheet with parchment.
5. Use lightly moistened hands to form about 2 tablespoons of the chilled mixture into a smooth cylinder.
6. Coat the Croqueta first completely in the flour, then the beaten egg. Drip off the excess egg, then coat thoroughly in bread crumbs. Place on the parchment-lined baking sheet and repeat with the remaining mixture.
7. Once the oil is 350˚F (180˚C), fry the croquetas in batches, being careful not to overcrowd, until golden brown and heated through. Gently turn as needed to evenly fry.
8. Remove to a towel-lined plate to drain excess oil and repeat with remaining Croquetas. Serve warm.